fya^gM C. BAYLOR

SPRING 1965 Bulletin No. 8

PART I: Geology and Urban Development PETER T.FLAW N Geology of Waco J. M. thinking is more important than elaborate

FRANK CARNEY, PH.D. PROFESSOR OP GEOLOGY BAYLOR UNIVERSITY 1929-1934

Objectives of Geological Training at Baylor

The training of a geologist in a university covers but a few years; his education continues throughout his active life. The purposes of training geologists at Baylor University are to provide a sound basis of understanding and to foster a truly geological point of view, both of which are essential for continued pro­ fessional growth. The staff considers geology to be unique among sciences since it is primarily a field science. All geologic research in­ cluding that done in laboratories must be firmly supported by field observations. The student is encouraged to develop an inquiring objective attitude and to examine critically all geological concepts and principles. The development of a mature and professional attitude toward geology and geological research is a principal concern of the department.

THE BAYLOR UNIVERSITY PRESS WACO, TEXAS BAYLOR GEOLOGICAL STUDIES IN COOPERATION WITH COOPER FOUNDATION

A SERIES ON

URBAN GEOLOGY OF GREATER WACO

PUBLICATION SCHEDULE

Part I: GEOLOGY Bulletin No. 8, Spring,

Geology and Urban by Peter T. Director, Texas Bureau of Economic Geology, Austin, Texas. of Waco by J. M. Burket, Professor of Geology, Tyler Junior College, Tyler, Texas.

Part II: SOILS Bulletin No. 9, Fall, 1965

Soils and Urban of by W. R. Elder, Field Specialist-Soils, Soil Conservation Service, Temple, Texas.

Part III: WATER Bulletin No. 10, Spring, 1966

Waters of Waco by H. D. Holloway, Geologist, Texas Water Development Board, Austin, Texas. Surface Waters of Waco by Jean M. Spencer, Resident Research Geologist, Department of Geology, Baylor Uni­ versity, Waco, Texas.

Part IV: ENGINEERING Bulletin No. 11, Fall, 1966

Foundation Geology in Waco by A. M. Geological Engineer, Chief of Foundations Section, U. S. Corps of Engineers, Fort Worth, Texas. Geologic Factors Affecting Construction in Waco by E. F. Williamson, Geologist, formerly Material Analyst, Texas Highway Department, Waco, Texas.

Part V: SOCIO-ECONOMIC GEOLOGY Bulletin No. 12, Spring. 1967

Economic Geology of Waco and Vicinity by W. T. Huang, Professor of Geology, Baylor University, Waco, Texas. Geology and Community Symposium bv authorities on Law, Appraising, Architecture. Public Works and other professions. Symposium R. L. Bronaugh, Professor of Geology, Baylor University, Waco, Texas.

Part VI: CONCLUSIONS Bulletin No. 13, Fall, 1967

Urban Geology of Greater and Recommendations by the Editorial Staff, Baylor Geological Studies, Bavlor Universitv, Waco, Texas.

i FOREWORD

The development and early growth of Waco Geological Studies provided free coordination, carto­ occurred primarily on the outcrops of the Austin graphic-field supervision, editorial service. Chalk and the Brazos Alluvium. geologically Since the project was initiated early in 1963, it related problems appeared in the early development has evolved in concept and scope. The number and of the city primarily because of the stable nature of nature of contributions expanded as the project ma­ the chalk and alluvium underlying most foundations tured. The URBAN GEOLOGY OF GREATER in the city; the light weight and simplicity of most WACO includes major contributions from the Bay­ early the relatively light loads on streets lor Geology Department, Texas Bureau of Economic and the uncomplicated nature of sewage and Geology, U. S. Soil Conservation Service, U. S. Corps pipe and the low demands of a small pop­ of Engineers, Texas Highway Department and Texas ulation for water, sand and gravel, sewage disposal Water Development Board. Shorter contributions and storm drainage. include papers by an architect, attorney, real estate During and after World War II, Waco expanded appraiser, public works engineer and others. from these stable outcrop areas onto the outcrop of In the spring of 1964, a series of eight public eve­ the unstable, incompetent shales of the Taylor For­ ning seminars were held at Baylor to provide con­ mation to the east and Eagle Ford Group to the tributors with an opportunity to present a summary west. This geographic expansion of Greater Waco of their reports for comments and discussion. A stu­ during the past twenty years has been accompanied dent seminar was conducted at the same time to by many new urban problems of geological origin explore all areas of urban activities which are related in addition to many existing problems which became to the earth sciences. critical with rapid urban population growth and Originally, the proposed Urban Geology report expansion. was scheduled to be released as a single volume. Among these important urban geological problems During preparation the various reports were expand­ are those involving sand and gravel, which are lost ed and complex illustrations were other pa­ to the area by unplanned city growth; foundation pers were solicited to cover additional areas of im­ problems, which result in the failure of foundations portance. Because of the increased scope of the in one area, in soil problems project, ten major and numerous shorter papers are involving corrosion of pipes, failure of foundations, included in the Baylor Geological Studies urban variation in excavation costs and drainage problems ; series. water supply problems, including surface and sub­ Beginning with Baylor Geological Studies Bulle­ surface sources, utilization and pollution; and the tin No. 8 (Spring, 1965), six successive semi-annual quality, quantity and location of economic rocks and Bulletins will include papers grouped according to minerals in the Waco region. Geology, Soils, Water, Geological Engineering, These and many other problems cannot be solved Socio-Economic Geology and Conclusions. Included adequately and economically without considering in the series are multicolor geologic, soil, isopach the role of the earth sciences. Responsible long- and structure maps (on U.S. Geological Survey range urban development must also involve other topographic base), charts, illustrations and tables of geologically related aspects, such as problems of various types prepared by the Baylor Geological legal nature, property evaluation, city planning, Studies student cartographic staff. Thirty-five recreation, beautification and development costs. hundred copies of Baylor Geological Studies Bul­ In recent years the Baylor Geology Department letins 8-13 (Urban Geology series) will be pub­ has received a growing number of requests for geo­ lished and sold for $1.00 each. Sale of URBAN logical advice the aforementioned areas of urban GEOLOGY OF GREATER WACO will be han­ development. Although Baylor geologists have sup­ dled by Baylor Geological Studies in agreement plied free consultation as a public service, there has with Cooper Foundation. developed an apparent need for more comprehensive The editorial staff and contributors intend to and accessible data on the total spectrum of earth provide a comprehensive series on Waco Urban science-urban relationships. The Baylor Geological Geology, which may also serve as a model for others Studies editorial staff decided in 1962 that a compre­ interested in this vital area of geologic application hensive on the Urban Geology of Waco and service. No precise estimate can be placed should prove an asset to the city and its citizens. on the value of supplied by governmen­ Late in 1962 a thorough survey was made to as­ tal agencies and individual researchers, or on the certain sources of earth science data pertaining to value of time donated by authors, editorial staff and the Waco area, as well as to locate published refer­ interested geologists. The Cooper Foundation grant ences on Urban Geology. Many city, state, and and the Baylor Geological Studies budget for the six federal agencies, as well as interested individuals, issues in the series will exceed amount were invited to cooperate in the project. which is conservatively estimated to be less than The Cooper Foundation, a private civic philan­ ten percent of the actual cost of the project if it had thropic foundation in Waco, was approached in been contracted at regular professional and commer­ January, 1963, for financial support to aid in the cial rates. preparation and of a Waco Urban Geol­ The editorial staff appreciates this opportunity ogy report. A detailed, budgeted proposal was ap­ to provide a public service for the citizens of Waco. proved by the foundation to cover the proposed cost We sincerely thank the Cooper Foundation, of and related expenses, totaling $7,000. University and the various State and Federal Agen­ Baylor University, through its press, accounting cies, as well as the many individuals, who made this geology department, and Baylor Geological series possible. Studies budget accepted the responsibility for the L. F. Brown, Jr., EDITOR remaining expense. The editorial staff of the Baylor Spring, 1965 ii BAYLOR GEOLOGICAL STUDIES

BULLETIN NO. 8

IN COOPERATION WITH COOPER FOUNDATION

A SERIES ON

URBAN GEOLOGY OF GREATER WACO

PART I: GEOLOGY

Geology and Development PETER T. FLAWN

Geology of J. M.

BAYLOR UNIVERSITY Department of Geology Waco, Texas Spring, 1965 Baylor Geological Studies

EDITORIAL STAFF

Lv. F. Brown, Jr., Ph.D., stratigraphy, paleontology O. T. Hayward, Ph.D., Adviser stratigraphy-sedimentation, structure, geophysics-petroleum, groundwater R. L. Bronaugh, M.A., Business Manager archeology, geomorphology, vertebrate paleontology James W. Dixon, Jr., Ph.D. stratigraphy, paleontology, structure Walter T. Huang, Ph.D. mineralogy, petrology, metallic minerals

Jean M. Spencer, M.S., Associate Editor Anita L. Reeves, B.A., Associate Editor Jerry L. Goodson, M.S., Cartographer O. Donald Baldwin, Assistant Cartographer

The Baylor Geological Studies Bulletin is published Spring and Fall, by the Department of Geology at Baylor University. The Bulletin is specifical­ ly dedicated to the dissemination of geologic knowledge for the benefit of the people of Texas. The publication is designed to present the results of both pure and applied research which will ultimately be important in the economic and cultural growth of the State.

photograph : Aerial view of Downtown Waco. Photograph provided through the courtesy of WINDY DRUM STUDIO, COMMERCIAL Waco, Texas.

Additional copies of this bulletin can be obtained from the Department of Geology, Baylor University, Waco, Texas. $1.00 postpaid. CONTENTS Page Schedule of urban geology series Foreworcl GEOLOGY AND URBAN DEVELOPMENT by Peter T. . 5 GEOLOGY OF WACO by J. M. Burket 9 Abstract Introduction Purpose Location Historical background ...... Acknowledgments ...... Physiography . . . . . - Structural geology 16 Framework of Central Texas ...... Geologic structure of Waco ...... Geologic structure and Waco development ...... Stratigraphy ...... Surface formations ...... 19 Quaternary System ...... 19 Recent alluvium ...... Brazos alluvium 19 Character and distribution . . . . . 19 Soils 19 Relation to urban development 19 Bosque alluvium ...... 20 Character and distribution 20 Soils 20 Relation to urban development . . . . 20 Pleistocene terraces ...... 20 Terrace systems ...... 20 Depositional characteristics .20 Age of terraces ...... 20 Brazos terraces ...... 21 Terrace levels ...... 21 Soils 21 Composition ...... 21 Relation to urban development ...... 21 Bosque terraces 21 Character and distribution ...... 21 Soils 21 Composition ...... 21 Relation to urban development ...... 21 Cretaceous System ...... 22 Taylor Marl 22 Original definition 22 Age and distribution . 22 Description ...... 22 Soils 23 Relation to urban development 23 Austin Chalk 23 Original definition ...... 23 Age and distribution 23 Description ...... 24 Soils 24 Relation to urban development 24 South Bosque Shale 25 Original definition ...... 25 Distribution ...... 25 Description 26 Soils , 26 Relation to urban development 27 Lake Waco Formation . 28 Original definition ...... 28 Distribution 28 Description ...... 28 Soils 29 Relation to urban development 29 Pepper Shale 29 Original 29 Age and distribution 29 Description 29 Soils 34 Relation to urban development .34 Buda Limestone 34 Original definition ...... 34 Age and distribution 34 Description ...... 34 Soils 35 Relation to urban development Del Rio Clay 35 Original definition ...... 35 Age and distribution 35 Description 35 Soils . . . . 37 Relation to urban development 37 Subsurface formations ...... 37 Georgetown Formation ...... 37 Original definition ...... 37 Age and distribution 37 Description ...... 37 Relation to urban development ...... 37 Edwards Limestone ...... 37 Comanche Peak Limestone ...... 38 Walnut Clay 38 Paluxy Sand ...... 38 Glen Rose Limestone 38 Hensel Sand ...... 39 Formation ...... 39 Formation ...... 39 Hosston Sand ...... 39 Pre-Cretaceous rocks ...... 39 References ...... 40 and conclusions ...... 41 Well localities 42 Glossary ...... 43 46

ILLUSTRATIONS

FIGURES Page 1. Index and regional geologic map, Central Texas .... 12 2. Physiographic map, Central Texas 13 3. Diagrammatic east-west cross section, Waco area . . . . 26 4. Foundation support strength of bedrock, Waco area ... 32 5. Difficulty of excavation of bedrock, Waco area . . ... 33 6. Infiltration capacity of bedrock, Waco area ..... 36

PLATES I. Geologic map, Waco West Quadrangle Pocket II. Geologic map, Waco East Quadrangle Pocket III. Structure map, top of Georgetown Formation, Waco West Quadrangle Pocket IV. Structure map, top of Georgetown Formation, Waco East Quadrangle , . . Pocket V. Type electric and Hthologic well log, Waco area . . . Pocket

1. Geologic time scale ...... 18 2. Sequence, classification, description and critical properties of geologic formations, Waco area ...... 30 and Urban

PETER T. FLAWN Director, Bureau of Economic Geology, The University of Texas, Austin, Texas

"The problem of uncontrolled population growth emerges as one of the most critical issues of our time since it influences the welfare and happiness of all the world's citi­ zens. It commands the attention of every nation and society; the problem is no less grave for the technically advanced nations than for the less

President National Academy of Sciences, 1963

The problems of cities are the problems of population engineering are the most important areas for scientific growth. It is in the cities that the spectre of a rationed and engineering research in the coming decades. It is future is first future where there are so many urgent that we intensify and expand our present feeble people that there is not enough to go around, not enough efforts in these fields—in training and in research. It land or living space, not enough clean air, not enough is not a matter of whether we can such ex­ water, not enough food, not enough goods or services. in current debates over sending expeditions There are bacterial cultures that multiply to the point into is a matter of survival and to hell with where their population exceeds the food reserves of their the environment; thereupon they starve to death. There The city has a gargantuan appetite for resources of are bacterial cultures that multiply to the point where all kinds. Mineral stuffs and food flow from the the toxic products they produce so befoul their environ­ land into the city. There is a return of contamina­ ment that they poison pneumococcus, for tion from the city to the land. The city is the nucleus example, produces enough peroxide to kill itself in a of the contamination, and the nuclei themselves are period of 24 hours if that poison is not removed from spreading. In the year 2000 cities with populations of the system. Commonly, the self destruction results 25 to 50 millions will not be unknown. Paradoxically, from both mechanisms operating simultaneously. as we break through new frontiers on every side and To draw an analogy with the human culture is not the average citizen has a greater appreciation for science pleasant but I think it is clearly indicated. Only the and engineering than ever before, we seem to be entering time scale is Our population growth, together a dark or twilight age as far as appreciation for and with the industrial and agricultural activities necessary understanding of the land is concerned. I do not mean to sustain it, has already put great pressure on re­ that understanding and appreciation do not sources and has gone far toward increasing the toxicity mean they do not exist for the great mass of the people. of our environment. We are stuck with the old com­ Resources specialists and conservation groups are more pound interest geometric knowledgeable than ever before. But the mass of the and there is no way to repeal it. If population increases people are turning their faces from the land to the city, at the rate 1.5 percent per in the United and the new generation does not know the land. This will double every 47 years. Through public is perhaps less true in Texas and the western states health and safety campaigns, governments fight death than elsewhere in the country, but it is true in the metro­ at every turn but birth is such a sensitive area that few politan centers of Texas. nations have national population policies. We have Well, so what? Let's be nostalgic and sentimental reached the point where growth is not, as it always has about the land, and then let's forget it and think about been in the past, necessarily a good thing. hard facts. In my opinion, as a direct result of population growth, The earth and the sun and the people are the ultimate the areas of resovrces and science and resources. As the population grows, more pressure is put on the resources of the earth and there is less of an address made to a Gcosciencc and margin for waste. And as the population grows, violent Urban Baylor University, Waco, Texas, Feb- 13, 1964. or catastrophic natural end members of 6 BAYLOR GEOLOGICAL STUDIES

the gamut of natural processes which tectonism, the commodity is haulage at 40 miles the cost mass wasting, sedimentation, and atmospheric dynamics transport is twice the value of the commodity at the far more damage than ever before. This is source. When multiplied by a factor of thousands of of the complexity of the system where so many tons, the cost increment is substantial indeed. This is factors are interdependent and all depend on a con­ another way of saying that a large deposit of sand and tinued flow of power, transportation, water, sewage, gravel within the city limits is a valuable asset, and the continued stability of the earth's surface. As a similar deposit 100 miles away may be worthless. the system grows more complex, so it grows more vul­ Construction materials are already in short supply nerable, and so the better must be our engineering. around many large cities and growing smaller cities. Engineering improves as science advances. The en­ For example, in Texas in 1963 the total value of sand gineer asks scientist asks "why?" True, and gravel produced was over half a million dollars less the engineer can deal with most systems without under­ than in 1962, while all other construction minerals standing them but he must then work empirically with­ showed increases. The decline was not due to a lessen­ out a precise knowledge of limits, and therefore his ing of demand. In some areas, sand and gravel deposits margin factors are large and expensive and his solu­ have been depleted so that they are being replaced in tions sometimes more complex than necessary. If their former markets by higher priced crushed efficient engineering is the goal, and it must be, then Several years ago, leaders of the Denver, Colorado,' natural processes must be thoroughly understood. metropolitan area became concerned about the decline of sand and gravel reserves in the area. A study was Geological considerations are important in the de­ initiated by the Intercounty Regional Planning Com­ velopment of a city in two broad areas Resources mission. Its report Original reserves and (2) Municipal Engineering. available to the city were million tons. (2) Re­ Water is the prime municipal resource. With few ex­ maining were 244 million tons (24 years supply at cur­ ceptions, cities were built where there was a supply of rent rate of exploitation). (3) Since 1950, 50 million water adequate for the original demand. However, tons had been produced but because of new construction nearly all cities have outgrown their local water supply built on sand and gravel deposits, available reserves had and must transport water. And as cities become larger, diminished by 250 million tons. The Commission recom­ their water appetites become more voracious. Two mended that land use be regulated by zoning to protect sources of water are available to a water and conserve sand and gravel resources. and ground water. As surface water supplies close to Construction materials are not as vital to a city as the city become inadequate, the city constructs new is water supply, and probably the same degree of control reservoirs and reaches farther afield to tap lakes and and supervision is not called for. Clearly, however, it rivers. Commonly this brings the city into conflict with is practical for a city government to be concerned with other prior users. Another solution to the problem is construction costs within its limits, and, therefore, it the development of well fields to exploit ground water is practical for a city to look to its reserves of con­ but not every city is fortunate enough to be located in struction materials. an area where there are large supplies of potable ground The planning group of a city that suddenly is con­ water. In the future some cities will be forced to con­ cerned about depletion of sand and gravel or crushed vert saline or brackish sea or ground water for municipal stone sources cannot simply find the least desirable use. Pilot plants to remove salts from such waters are land in the old zone it for quarry already in operation. Research and development in this sites. Resources are where they are and cannot be area are at a high level. Of course all of these projects created by legislation. The sand and gravel resources which involve construction of reservoirs and aqueducts, are in the terraces along the river that are being sold drilling of wells, and installation of plants to manu­ to developers for $8,000 per acre. Politically, there is facture potable water from saline water raise the cost not a chance in the world that a prime real estate area of water. Now the great metropolitan area of Southern will be zoned for quarry development. Ten years is reaching hundreds of miles into the north­ earlier it could have been done, but the city planners ern part of the State, at a cost measured in billions of did not have a geologic map so they did not know dollars, to meet its needs for water. Usually, because we live in a democracy, a great city which counts its voters the and gravel was there; (2) not know the in the millions is a political power and can achieve its total reserves then being exploited or the rate of con­ sumption so they could not predict the shortage that was

imminent. In fact, they not and still do not know Less critical city resources are the construction ma­ anything about the resources of materials terials. The kind and quantity of construction materials in and around the city. The same kind of advance available certainly control a city's appearance and affect planning used by city departments concerned with municipal engineering. Brick and tile clays, dimension water, power, sewage, and parks must be applied stone, concrete and gravel and crushed to construction material resources. If sand and gravel examples of this kind of resource. are hauled in from distant points, the price of concrete The resources which are of concern to a will go up, construction costs will go up, and the bills and construction measured in per will go up. Perhaps that school addition will not be 1,000 gallons, cents per yard, or cents per ton. They built, perhaps the public education facilities will be are commodities which are used in large volumes but rated as inadequate, perhaps the big plant will go else­ which have a low value per unit of production. Of para­ where. mount importance, then, is the location of the Demographers predict two giant cities or megapoli proximity to a city's growing parts. If a commodity in one along the Gulf Coast between Houston has a value of $1.00 per ton at the quarry, and if it and Corpus Christi and one on the black prairies be­ costs per ton-mile to transport it, one can easily see tween San Antonio and Dallas-Fort Worth including that at the end of a haul, one-half the cost of New Braunfels, San Marcos, Austin, Temple, and GEOLOGY AND URBAN DEVELOPMENT 7

Waco. In the United States, about 1 million acres of Or perhaps the jail is a disgrace. It is easy to land per year are being converted to home sites. Bear point to spectacular events, such as a dam failure, and in mind that most of this land is in and around existing imagine the tangible and intangible cost to a city. But population centers where the mineral producer com­ the nonviolent and unspectacular events probably have petes for land. Every mile of new federal highway con­ cost more. Consider the bridge that cost $700,000 in­ sumes 40 acres. The answer to the urban land shortage stead of $300,000 because of inadequate geological ad­ is multiple use. Mineral construction materials can be vice on location of abutments and/or test borings. harvested, and then the land can be made available for To me, it is a fantastic truth that most cities do not construction sites. have a geologic map and do not employ a geologist. Of course, there will always be resistance to planning The use of a geological consultant (except on special it is true that exercise of eminent domain by a problems) is not the solution. What is needed is con­ city can be reckless. The individual whose land is tinuing geological supervision to permit day-to-day condemned by the city rarely feels that he has gotten a accumulation of data so that the city can take advantage square deal. But in the future we will have to support of and exploit its terrain, foundation materials, and planned urban complexes or live in chaotic urban resources. In particular, the geologist's job should be jungles such as now exist around the old the construction and maintenance of an accurate large- Chicago and New York. It will be much cheaper to scale geologic map. Such a map will pay for itself time plan now. Los Angeles has attempted to bring mineral and time again, and for the geologist as well. When deposits into its plans for the future. The city surveyed not employed on geological tasks, the geologist can run sand and gravel deposits in the San Fernando Valley, survey lines or do other routine engineering work. The evaluated them by drilling, and zoned a number of geologist is necessary here because geologic maps made gravel pit sites. After the deposits are quarried, the by engineers are notoriously inadequate. The engineer pits will first be used for refuse disposal and then re­ can log holes or describe sample pits, but the inter­ stored for urban use. pretative part of the map between holes is and should Under the general heading of municipal engineering be the geologist's job. we consider what kind of geologic foundation the Such a map, like a mine map, must be kept up to city rests on, (2) the structural fabric of the foundation, date with every new excavation dug or hole bored. It (3) the porosity and permeability of the foundation. thus comes close to being a fairly accurate model of the (4) the topography and climate, and (5) the tectonic surface. The city geologist should inspect every excava­ stability of the area. If we are going to pile great tion. Although hundreds of excavations are made in a weights on top of rocks, anchor bridges or dams to city in the course of a year, they are rapidly filled. rocks, drill holes and dig tunnels in rocks, lay slabs What a tragedy the information is lost. What a tragedy on top of rocks, or dispose of waste in rocks, we must the city does not realize how much it needs these data. know how the rocks or soils are going to react under a What good is the map? How can it pay for itself? variety of conditions, e.g., when they are very dry or Let us forget for a minute its obvious value in water and very wet, when they freeze or thaw, when the slope construction material resource evaluation and consider is flat to gentle or very steep, and when they are sub­ only engineering value. When a contractor bids blind jected to earthquake or gravity stresses. (I am, of on a city excavation job, for example, he bids high course using rock in the broad sense to include earth enough to cover unforeseen problems of water floods, materials in general.) The availability of these data not hard rock, heavy ground, etc. If, however, the city lets only determines where, if anywhere, there can be high- a bid on an excavation job and specifies the job as re­ rise structures on the city availability of moval of so many yards of a certain kind of rock, the these data can be a matter of life or death. This is bids are lower because the con­ particularly true in cities where pressure for land has tractor can accurately calculate his costs. Savings over resulted in construction on unstable slopes, in known a period of years can be very large. slide areas, and over active faults. If poorly engineered A geologic map is the difference between groping in city public works projects induce slope failure or slides, the dark and working in a lighted room. With an the city's liability may be a matter of millions of dollars. up-to-date large-scale geologic map, a few confirmatory These are all rather obvious points. What is not auger holes may do the job and make unnecessary a generally appreciated is the eflfect our degree of knowl­ $20,000 test-drilling The scale of the map, edge about these foundation properties has on costs. of course, depends on the kinds of problems and may All engineering projects cost money, and if because of vary from one part of the city to another. In one large inadequate geological knowledge a bridge costs more U.S. city, areas are now being mapped as 400 feet to than it should, or a disposal pit leaks, or a dam fails and the inch. must be repaired, the city pays the bill. It pays with Most publicly financed geologic Federal revenue derived from taxes or bonds. And if, because and State, have trod lightly in the area of urban geology of mismanagement and lack of appreciation of geological because of the political sensitivity of some aspects of it. aspects of engineering problems, the city is overloaded To designate an area of a city as possessing undesirable with too-high taxes and heavy bonded debt, the city's or unsafe foundation materials is to invite political growth rate can be adversely affected. For example, if attack by the associated landowners. To classify an construction costs are high because city planners were area as a potential slide area prior to the catastrophe ignorant of the need to think ahead for construction is likewise an invitation to trouble. materials or if the city has in the past paid more for The only conclusion that can be drawn from a study streets, sewers, bridges, tunnels, and public buildings of the role of geology in urban development is that the because of their engineering department's lack of ap­ city with a geologist or a geological department will preciation of the geological side of municipal engineer­ be a more efficiently run city in a better position to meet ing, the city may have been unable to afford a modern the demands of the future when an urban area with a auditorium. Or perhaps the by-pass was never com- population of 1,000,000 is a small town.

Geology of Waco

1 M. Professor of Geology, Tyler Junior College, Tyler, Texas

ABSTRACT

Geologic factors control or substantially affect the growth systems resulting in pollution of lakes and streams. Shock and development of a city. Rock materials, soils, water, building waves from blasting are conducted or guided along fault sites, landscaping, and certain legal and socio-economic problems zones, creating asymmetric blasting hazard zones. Fault and are related to geology. This report on the geology of the City joint trends are zones of weakness, which can be utilized in of Waco is designed for use by city residents, builders, in­ quarrying and excavation. Major faults affect artesian water dustrialists, and city planners. It is hoped that a better under­ production from Lower Cretaceous sands, and faults may modify standing of the local geologic framework improve urban water chemistry by contaminating potable aquifer water with planning, structural designs, conservation, proper utilization of saline water from overlying and underlying formations. resources, and other factors vital to Waco development. Formations, which crop out in the Waco area, include This is the first of a six-part series on the natural environ­ Quaternary alluvium and terrace deposits of the Brazos and ment of the City of Waco. The geologic report (Part I) is Bosque rivers; Upper Cretaceous (Gulfian Series) Lower divided into five Introduction, Physiography, Struc­ Taylor Marl Member of the Taylor Formation, Austin Chalk, tural Geology, Stratigraphy, and Summary and Conclusions. South Bosque Shale, Lake Waco Formation, and Pepper Previous geologic research in the Waco area has been largely Shale; and Lower Cretaceous (Comanchean Series) Del Rio scientific and primarily of interest to geologists. In the current Clay. study, aspects of geology are emphasized, which are most crit­ Subsurface formations (fig. 3) of the Waco area include in ical to urban development. descending order the Lower Cretaceous Georgetown Limestone, Waco is situated principally on the Bosque escarpment, which Edwards Limestone, Comanche Peak Limestone, Walnut Clay, separates the Black and Grand prairies of Texas. The major Paluxy Sandstone, Glen Rose Limestone, Hensel Sandstone, part of Waco rests upon the Black Prairie. Principal drainage Pearsall Formation, Limestone, and Hosston Sand. Paleo­ in Central Texas is furnished by the Brazos River and its zoic rocks of the Ouachita foldbelt underlie Cretaceous rocks major tributary system, the Bosque River system. Waco and in the Waco area. Cottonwood creeks drain most of Waco west of the Brazos Surface or outcropping formations in the Waco area are River. most significant to city growth and development because of their Waco is underlain by eastward dipping bedrock of the Gulf eft'ect or control of topography, engineering properties, soils, Coastal Plain. This homoclinal structure is broken in the Waco construction, and other urban problems. Subsurface formations, area by the complex Balcones fault system, which bisects the however, are important to urban development only if they pro­ city a north-south line. duce economic rocks or minerals along the outcrop within The position of the Bosque escarpment or fault-line scarp reasonable hauling distance of Waco, produce potable water in coincides with major faults of the Balcones system, which are the Waco area, or provide for underground disposal of dan­ illustrated on geologic maps I, II) and on structural gerous wastes. maps IV). Faults and joints, which are clearly and Bosque river alluvial evident on aerial photographs, are most conspicuous in areas deposits occupy the lowest areas in Greater Waco. Alluvial of Austin Chalk outcrop. The age of Balcones faulting in the areas are subject to occasional flooding, and channel migration Waco area has not been precisely determined, but indirect introduces risk in development. Alluvium ranges widely in evidence suggests that faulting continued from early Cretaceous foundation and infiltration properties (table 2). Pointbar de­ to middle Tertiary time. posits are well drained and filled meander scars are Complex fault patterns and a variety of rock formations in poorly drained. Ground water from alluvial deposits is polluted, the Waco area have resulted in problems of foundation design, although water is available in moderately large quantities ground water and drainage, corrosion, septic and sewage dis­ (particularly from Brazos River alluvium). posal, and excavation. Engineering characteristics of bedrock Brazos and Bosque terraces are composed of sand and formations are products, therefore, of rock types and super­ gravel. Terraces occur from 20 to feet above present river imposed structural (faults) complications. level. Terraces provide gravel and sand, provide limited Along major faults in Greater Waco, Austin Chalk is in amounts of seasonal ground water (usually polluted), and fault contact with Taylor Marl and the Eagle Ford Group. provide reservoirs for underground disposal of minor quan­ Foundations may, for example, rest partly upon Austin Chalk tities of waste water. and partly upon Taylor Marl, commonly resulting in foundation Brazos River terraces furnish excellent commercial siliceous failure (or over-design). Soil thickness, which is dependent sand and gravel, some ground water (polluted), and stable upon weathering rates, is controlled by faults and joints. foundation sites for light structures. Bosque terraces furnish Septic sewage effluent is conducted by "piping" along fracture limited supplies of exceptionally good base material (consisting 10 BAYLOR GEOLOGICAL STUDIES of gravel wi clay provide limited amounts no fluid, and it forms a highly corrosive environment for of water (polluted), provide for modest underground disposal buried pipes. Pepper Shale is exposed only in the extreme south­ of waste water, and normally furnish stable building sites for western part of west Waco. light structures. . Del Rio Clay, which underlies Pepper Shale, is composed of Cretaceous rocks Greater Waco gray, calcareous, plastic clay with rare discontinuous stringers are bedded limestones and shale. The youngest Cretaceous of fossiliferous limestone. In the Waco area Del Rio Clay is formation in the Waco area is Taylor Marl, which crops out commonly exposed in excavations in the extreme northwestern throughout east Waco although it is commonly overlain by part of west Waco. In its engineering properties, Del Rio Clay Brazos terrace and alluvial deposits. The Lower Taylor Marl resembles the Lower Taylor Marl Member. Del Rio is Member of the Taylor Formation is a highly highly plastic when wet, forms corrosive soils, and is im­ calcareous clay, which is plastic when wet. permeable to drainage or infiltration. The formation is easily Some unweathered Taylor Marl will support up to ten tons excavated and the clay fails by slumping even on gentle slopes. per square foot, but commonly support strengths are much less. In Greater Waco rocks older than Del Rio Clay occur only Foundations and footings in the Taylor should extend well in the subsurface. These buried formations include in descending unweathered material, and excavations should be closed im­ order Georgetown Limestone, Edwards Limestone, Comanche mediately to prevent swelling of bentonitic clays in unweathered Peak Limestone, Walnut Clay, Paluxy Sand, Glen Rose Lime­ marl. Foundation failures are common in weathered marl be­ stone, Hensel Sand, Pearsall Formation, Formation and cause of its plastic nature and high ratios. Buried Hosston Sand. structures such as septic tanks, storage tanks, or bomb shelters Georgetown Formation, crops out in the Washita may be crushed by expansion of clays. Excavations and Prairie immediately west of the Bosque escarpment, exhibits gentle slopes may be unstable, especially if cuts and slopes are high support strength. It resembles Austin Chalk in most of its in Taylor fill material. Taylor Marl does not produce water, properties. Georgetown Limestone produces essentially no water and it will not effectively absorb septic sewage unless drainage in the Waco but it furnishes a source of marginal road fields are very large. Thin veneers of terrace deposits along the Taylor Marl outcrop cause wide variation in mechanical prop­ base material. erties in local areas. Faults and joints further complicate urban Edwards Limestone crops out in the Lampasas Cut Plain, problems along the Taylor Marl outcrop. 20 miles west of Waco. It furnishes dimension stone and Austin Chalk crops out throughout much of west Waco. It crushed rock for the Waco area, and the Edwards Limestone provides fewer problems in foundations and septic disposal produces very limited quantities of water in the Washita systems and more difficulty in excavation than any Cretaceous Prairie immediately west of Waco. formation in Greater Waco. The formation is composed of Comanche Peak Formation, which crops out along the hill alternating beds of resis'.ant white chalk and less resistant slopes in the Lampases Cut Plain, is composed of soft, gray, gray marl, which form very stable foundation conditions. marly limestone. It has no economic value, and the formation Normally soils on Austin Chalk are so thin that they are does not contain water in this region. removed even in light construction. Soils derived from Austin Walnut Clay crops out in valley floors of the Lampasas Cut Chalk have extremely high shrink-swell ratios, and may cause Plain. It is dominantly clay, and the formation has no major founda'ion problems where they are sufficiently thick. economic value except to support agriculturally important soils. Austin Chalk will support steep cuts and banks, can be Paluxy Sand contains some potable water north and west of quarried only with difficulty by conventional operations, and Waco, but it pinches out southward near Waco. It produces will support openings of considerable size. The formation small quantities of oil in the South Bosque field immediately produces some polluted ground water, and it absorbs moderate west of Waco. amounts of septic sewage effluent. Fluid transmission withm Glen Rose Limestone is the thickest formation in the Waco Austin Chalk is complicated by fracture and joint systems. area (700 feet). It produces some sulphurous water, and it may The Eagle Ford Group underlies Austin Chalk. It is ultimately provide a reservoir for underground waste disposal into South Bosque Shale and Lake Waco Formation. South by means of wells. Bosque Shale, which is exposed along the face of the Bosque Hensel Sand is 70 feet thick in the Waco escarpment, is a dark gray to black, blocky, homogeneous shale. area, and it produces large quantities of potable artesian water. The upper 40 feet are essentially noncalcareous, and the lower Pearsall Formation is composed principally of sandy cal­ 120 feet are highly calcareous in the Waco area. The upper careous shale in the Waco area, and it does not contain sig­ noncalcareous part of the formation is used in expanded ag­ nificant quantities of water. gregate production and in cement. Sligo Limestone grades westward into sand in the vicinity Because of thin limestone beds in the upper and lower parts, of Waco. The formation contains no water in the area. the Lake Waco Formation has an even greater range of support Hosston Sand is the deepest and most productive of strengths than South Bosque Shale. In general Lake Waco Trinity aquifers in the Waco area. It is feet thick and outcrops support somewhat steeper faces and heavier founda­ contains SO feet of saturated aquifer sand. In the eastern part tion loads. In' limestone sections, some fluid will be absorbed, of McLennan County, essentially all public and ar­ but excessively large drainage fields are required for septic tesian wells produce from this formation. Hosston water is of sewage disposal systems. Lake Waco Formation excavates good quality. easily in the middle Cloice Member, but more difficulty Rocks older than Cretaceous age in the Waco area have is encountered when excavating the limestone sections of the been recognized in deep wells. These pre-Cretaceous rocks basal Bluebonnet Member and upper Bouldin Member. occur in the Ouachita foldbelt, and consist predominantly of Pepper Shale, which underlies the Lake Waco Formation, low grade metamorphic rocks of Paleozoic age. In extreme consists of blue-gray, highly plastic, noncalcareous clay. Pepper southeastern McLennan County about 30 miles from Shale yields plastically under minimum loads, and the shale rocks of possible Jurassic age overlie the Ouachita facies and slumps readily even on very gentle slopes. It absorbs essentially underlie Hosston Sand in deep wells. GEOLOGY OF WACO 11

An understanding of geology constitutes essential of Geology, Baylor University. These Baylor geology background for appreciating natural environment publications and open-file reports, which are available of a city. This review of the geology of Greater Waco to all citizens, include detailed studies of the geology of (fig. is designed to provide cultural and practical in­ Central Texas within at least a 50-mile radius of Waco. formation for urban planning and development. In this report each formation within the Waco The geology of the city constitutes the framework region (table 2) is described and particular emphasis is within which all other natural factors are developed. given to those exposed on the surface Earth materials are the principal raw materials for I, II). The geologic structure of the City of building. Soils result from weathering of rocks. Both Waco (fig. HI, IV) is described and special and subsurface hydrology are largely controlled consideration is given to construction problems (figs. by geology. Hydrology involves drainage, flood control, 4, 5, 6) which arise from in engineering and quality and quantity of water. Successful foundation characteristics of various rock formations. engineering depends upon an understanding of the Subsequent publications in this Urban Geology of properties of rocks or soils upon which structures are Greater Waco series {see Foreword) will consider to be built. Horticultural and topographic landscaping urban soil characteristics and problems of sur­ depend primarily on geological factors. Legal and face and subsurface water supply, contamination, drain­ socio-economic problems of many types are related in age and other related factors in the Waco detailed a greater or lesser degree to geology. geologic engineering and soil mechanics data related The report is divided into five major to construction in economic geology of such Introduction, presenting general information about materials as sand, gravel, Portland cement materials, Waco and its surroundings; (2) Physiography, the re­ expandable shales and brick clays in the Waco region; lationship of the topography to regional geology; (3) and socio-economic geologic problems involving such Structural Geology, the age, origin, distribution and areas as law, architecture, landscaping, appraising and importance of rock (4) Stratigraphy, a other professions. description of sequence, properties, distribution, origin, This study of the Waco area is based on extensive and physical characteristics of the local rock formations ; research of all available literature, maps, samples, and and (5) Summary and Conclusions, emphasizing geo­ aerial photographs, as well as extensive detailed logic factors of major importance in the growth and geologic field investigations. Surface geologic data have development of Waco. been compiled on geologic maps of the Waco area In order for this publication to have maximum use­ L II). fulness, it has been necessary to use some technical Subsurface structural geology for this report was terms. A glossary (p. 43) and tables (tables 1, 2) are mapped on top of the Georgetown Formation supplied for those not familiar with geological language. HI, IV) utilizing elevations and fault control ex­ trapolated from surface and subsurface data. The top PURPOSE of the Georgetown Formation was used as the datum because of its uniformity and continuity throughout The primary purpose of this report is the description the area, and because the formation can be easily of the surface and subsurface geology of the Waco recognized in the subsurface with both electric logs area (fig. 1) which will aid in the future development V) and drillers' logs. of Greater Waco. Survey of the geologic literature shows that the geology of Waco has been of interest for many years. LOCATION In his monumental work on the Grand and Black prairies (fig. 2), Hill (1901, p. discussed the The City of Waco, county seat of McLennan County, geology of the Waco area. Other important early con­ is located near the center of the county on the prairie tributors to the geologic knowledge of the Waco area lands of Central Texas (fig. 2). In 1960 the population include Pace (1921), Adkins (1923), and Deussen of Waco was approximately 100,000. Waco is the (1924). Later significant contributions include many center for another 50,000 people in Central publications and open-file reports by the Department Texas. In this report Waco is generally defined as the area of the East and West Waco quadrangle maps Burket completed the initial study of the Geology I, II) published in 1957 by the United States Geolog­ of Greater Waco in as a master's thesis at Baylor Univer­ ical Survey. These quadrangle maps include a rectangu­ sity. With financial support from the Cooper Foundation, Burket lar area of slightly more than 125 square miles extend­ updated the study during the summer of 1963. Professor T. ing 14.7 miles east-west and 8.6 miles north-south. Hayward, Baylor Geological Studies staff, extensively revised and updated maps and manuscript early in The maps include Waco and Fig. 1. Index and regional geologic map, Central Texas. GEOLOGY OF WACO 13

Fig. 2. Physiographic map, Central Texas. 14 BAYLOR GEOLOGICAL STUDIES

way, Beverly Hills, as well as Lake Waco about 1850 and continued as the principal type of and the Municipal Airport. agriculture on the prairies until about 1880. McLennan County (fig. 2) is approximately 38 Range cattle were the so-called Texas Longhorns, miles long and 29 miles wide, and it includes an area of unimproved stock originating from cattle brought to 1,034 square miles. The eastern three-fourths of the North America by the Spaniards. During these early county is on the Blackland Prairie of Texas, a physio­ times the prairies were generally considered for graphic subdivision named for dark-colored soils on an farming, probably because of the distance from wood area of low relief, and the western one-fourth is located and water, as well as the lack of implements suitable on the Grand Prairie, a physiographic subdivision for tilling the clayey soil. Over 1,000 slave laborers marked by shallow calcareous soils (idem). The long farmed vast acreage in the Brazos River alluvial bottoms axis of the county is at right angles to the general (fig. 2) prior to the Civil War (Soil Conservation southeastward course of the Brazos River. Service, 1959, p. Waco is the center of a rich farming region. Some Waco was surveyed in 1849 and soon became a 875 square miles of McLennan County are prairie thriving community. The location a good lands and most of the prairies are now in cultivation. spring and high ground. Waco was established near a Several highways and railroads pass through Waco favored crossing of the Brazos River on the main travel assuring adequate transportation for this Heart of route from San Antonio to North Texas. Texas area. McLennan County was organized in from parts The Waco region has a humid subtropical climate of and Robertson counties (Conger, 1945, p. and is near the eastern margin of the semiarid West 38). The first bridge across the Brazos River was the Texas region. Summers are long with relatively high 1870 suspension bridge at Waco, which is still in use. temperatures much of the winters are short and Railroads reached Waco in 1881 and Baylor University mild. Significant freezing weather occurs only during moved to Waco in 1889 (idem, pp. 15-26). January and February. Cold spells normally last less Since 1900 cotton has been the dominant crop on the than a week, and are succeeded by periods of cool Blackland Prairie (fig. 2), a gently rolling prairie pleasant weather.. Occasional rainless periods of several underlain by clays, marls, and limestones. At various months can be expected, but an annual rainfall of 32 times, notably in the early twenties, cotton crops oc­ inches is average. Generally, enough rainfall occurs to cupied as much as 80 percent of the cultivated land on permit good growth of crops such as cotton and this prairie. Approximately 75 percent of the Blackland sorghums, but poorly distributed rainfall during the Prairie was cultivated until about 1925. There has been growing season frequently limits corn yield. Moderate approximately 33 percent reduction of cultivated acre­ fall and winter rainfall with low evaporation enables age in the Blackland belt of McLennan County since soils to absorb and store a large supply of moisture. 1925. Reduction of the cultivated acreage has coincided with expansion of livestock production.

HISTORICAL BACKGROUND ACKNOWLEDGMENTS The City of Waco occupies the site of two The writer acknowledges the assistance and continued El Ouiscat and Flechazos, which in the latter support of Professors O. T. Hayward, who suggested part of the eighteenth century were occupied by the this project and significantly contributed to field studies, agricultural Hueco (Tawakoni) Indians. According to cartography and manuscript revision, and J. W. Dixon, Stephen F. Austin, the main village population was Chairman of the Geology Department, Baylor Univer­ about 100 in 1824. The Hueco were reported sity. Additional acknowledgments are due R. L. Mc- to have grown peaches and corn near Waco. Cultivated Kinney and associates of the Waco District, Texas areas evidently were small and restricted to sandy Highway Department, for the use of Highway Depart­ soils on low terraces or on the flood plains along the ment information and for aid in solving en­ Brazos River (Adkins, 1923, p. 7). countered during the project. The Soil Conservation The first permanent white settler was George Barn­ Service, United States Department of Agriculture, ard, who established a trading post near the mouth of contributed soil information on the Waco area. H. D. Trading House Creek in 1842 II). Survey of the Texas Water Development Board, con­ T. J. Chambers grant in 1832 resulted in the pri­ tributed sub-surface data on the Hosston Formation. vate ownership of land. Included in the Chambers During the summer of 1963, funds provided by the grant was the south half of modern Waco. By 1836 the Cooper Foundation supported extensive revision and Republic of Mexico had granted all of the area near updating of the geological study of metropolitan Waco. Waco and within 10 miles of the Brazos River. George Chief cartographer, Jerry L. Goodson and assistant B. Erath, the "father of Waco," was one of the Rangers Don Baldwin, Department of Geology, Baylor Uni­ who helped establish Fort Fisher near Waco in 1837 versity, prepared all maps and illustrations with the (Conger, 1945, p. 14). financial support of Baylor University and the Cooper Stockmen started moving into the area about Foundation. Professor L. F. Brown, Jr., Department when Neil McLennan, for whom the county is named, of Geology, Baylor University, coordinated various established a ranch headquarters west of Waco on the aspects of the project during the summer of 1963 and South Bosque River. Extensive cattle ranching began throughout preparation of the final report. GEOLOGY OF WACO 15

PHYSIOGRAPHY

The City of Waco (fig. 1) is situated on the interior South Bosque River, which receives the drainage of the of the Gulf Coastal Plain and is underlain by entire Bosque system, empties into the Brazos in the eastward dipping Upper and Lower Cretaceous (table northern part of Waco I). The South Bosque bedrock. River closely follows the base of the westward facing Most of Waco (the eastern four-fifths) is situated on Bosque escarpment. the Prairie (fig. 2), one of the major geo­ Waco storm drainage is carried principally by Waco graphic regions of Texas. This north-south trending Creek which heads west of Heart O' prairie about 50 miles wide is underlain by marls, Texas fairgrounds in northwest Waco. The creek clays, and limestones of the Eagle Ford Group, the flows southeastward to Beverly Hills, where it changes Austin Chalk and the Taylor Marl (table 2). Some its course to the northeast and parallels the M. K. T. of the forested sandy Brazos terrace uplands and railroad tracks. Waco Creek meanders northeastward Brazos River bottoms or alluvium are included in this around Bell's Hill, and at Fourteenth Street part of belt, although they are of a different geologic origin. its discharge is routed underground through a flood These sandy terrace soils and alluvial soils support relief channel along Clay Avenue to the Brazos River. extensive timber belts. South and east of the junction with the flood relief The westernmost portion of Waco is on the Washita channel at Fourteenth and Clay, Waco Creek flows to Prairie (fig.. 2), a portion of the larger Grand Prairie, the Baylor campus where it is again routed under­ which is a major geographic division extending through ground between Fifth and Third streets. It enters the the Central Texas region. The Washita Prairie is River immediately east of the Baylor campus. underlain by limestones of the Washita Group (table Some drainage formerly entering Waco Creek has 2) . The region is a maturely dissected rolling prairie diverted southeastward along Twenty-sixth Street with shallow calcareous soils, and it differs from the to Primrose Avenue and then northeastward to the Blackland Prairie which has gentle topography and Brazos River. deeper clayey soils. West of the Washita Prairie is a The area southeast of the city is drained by Cotton- subdivision of the Grand Prairie, the Lampasas Cut wood Creek which originates south of Plain (fig. 2), a dissected plateau capped by Edwards Veterans Hospital and flows in a remarkably straight Limestone. eastward course until it empties into Eastland Lake, The boundary between the Washita and Blackland an abandoned gravel pit where both runoff and ground prairies (fig. 2) is marked by the Bosque escarpment, water accumulate. a northwestward facing cuesta and fault line scarp Flanking the Brazos River and its larger tributaries which extends across the northwest part of Waco in the Waco area are extensive stream I). This prominent stair-stepped, fault-controlled terraces. These may be divided into two groups: (1) topographic feature is a portion of the longer White Low terraces adjacent to present streams Rock escarpment, which has a northeast trend across (an aggregate area of about 40 square miles) ; and (2) Central Texas. Throughout much of the length of the remnants of old high gravel and sand terraces (Qbr2, Rock escarpment, the Austin Chalk caps the which cap many higher stream divides, highest parts of the scarp. Where the escarpment has especially east of the Brazos River (an aggregate area two topographic steps, the lower one is held up by of about 30 square miles). limestone beds in the Eagle Ford Group (table 2). The terraces range from extensive flats less than 30 The Waco region is drained by tributaries of the feet above the present flood plain to moderately dissected Brazos River II), which bisects the city from high terraces more than 200 feet above the present northwest to southeast along a broad flat alluviated Brazos River. Minor drainage systems dissect the valley. The Brazos floodplain and alluvial deposits vary various terrace levels. Older, higher terraces are ex­ from one mile wide in the northwest to four miles wide tensively dissected and frequently to distinguish in the southeast, and the river traverses the outcrop of topographically. both resistant and non-resistant strata. The vallev Between Waco and Asa (southeast of Waco) various apparently developed on a higher land surface, and the terrace flats extend along the west side of the Brazos Brazos maintained that general course as the land was River. On the east side of the river equivalent terraces lowered by erosion. The large deflection in the Brazos occur between Tehuacana Creek and the Brazos River channel north of the city, which is called Stein­ River Some of eastern Waco is built on beck Bend, is probably fault controlled. these terraces. Other extensive terraces occur on the On the Black and Grand prairies (fig. 2) where west side of the Brazos River north of Waco and many tributaries of the Brazos River have developed on along the north and west sides of Lake Waco. Along outcrop belts composed of weak rock, the drainage the present courses of the Brazos and Bosque rivers displays a trellis pattern characteristic of a belted are other extensive bottomlands or floodplain and coastal Locally, in the eastern part of the Waco alluvium (Obrf, Qbof, area where the relatively uniform non-resistant lower of the Taylor Marl crops out, a more dendritic drainage pattern has developed. The Bosque River system (fig. 2) is the largest tributary of the Brazos River in the Waco area. The 2Refer to map symbol on I, II. 16 BAYLOR GEOLOGICAL STUDIES

Highest elevations I, II) occur in the western­ to as low as 366 feet east of the Brazos River near most part of the city where the maximum elevation is Tehuacana Creek. Another area of low relief lies within feet ahove sea level. This western section of the the area bordered by Washington Avenue on the north, city is underlain by Austin Chalk which supports the Twenty-third Street on the west, and Franklin Avenue crest of the Bosque escarpment. East of the Bosque on the south. escarpment crest, the land is inclined gently eastward Southwest of downtown Waco is a prominent high on the dip slope of Austin Chalk. This eastward slope area (almost 500 feet elevation) known as Bell's Hill. is interrupted by local stream dissection, which creates From Bell's the land surface slopes gently east­ gently rolling topography. Lower elevations in the ward to the Brazos River. Other areas above 550 feet city range from 414 feet at the city square and 380 elevation lie along the Bosque escarpment in Woodway feet between Baylor University and the Brazos River and in the Veterans Hospital area.

STRUCTURAL GEOLOGY

FRAMEWORK OF CENTRAL TEXAS

Waco is situated on eastward dipping bedrock of belt (figs. 1, 3) suggest possible genetic relationships the Gulf Coastal Plain (fig. 1) where Cretaceous and (Hayward, 1957, p. 62). Tertiary rocks (table 1) crop out in belts parallel to The Ouachita (fig. 1), an ancient buried the Gulf Coast. Paleozoic mountain system, has been traced by means Strata of the coastal plain occur in ofiilap super­ of well records from the surface of southeastern Okla­ position, like shingles on a roof, with the outcrop of homa under Cretaceous rocks Waco, southward each younger bed progressively offset toward the coast. around the eastern and southern flanks of the Llano Each formation forms a truncated wedge and each uplift, then westward to the Marathon area where it normally thickens coastward. is again exposed at the surface 1961, p. 122). The homoclinal structure of the Gulf Coastal Plain Folding and faulting in the Ouachita Mountain system is broken in Central Texas by a complex pattern of en generally terminated by late Pennsylvanian time (table faults of the Balcones fault zone (fig. 1). Therefore, faults of the Balcones system are not IV). This fault zone, mapped in detail by related to active Ouachita folding. The Balcones fault (1961), marks the approximate boundary be­ system follows the course of this more ancient buried tween outcropping Lower Cretaceous strata of the mountain belt, and the two systems of difiierent age stable Texas craton to the west and more steeply are apparently structurally related. The Ouachita eastward dipping Upper Cretaceous rocks of the Fast system (figs. 1, 3) may have served as a fulcrum be­ Texas basin. tween the more stable Texas craton to the west and The Balcones fault zone (fig. 1) extends from near the subsiding East Texas basin. The Ouachita fold- Uvalde to the vicinity of Dallas. Major faults of the belt, therefore, may be responsible for localizing later Balcones system in the Waco area (fig. 3; faulting along this zone (or Paleozoic fulcrum) where IV) are down-thrown to the southeast with as much as tensional forces were created in the overlying Cre­ 260 feet of vertical displacement. The date of this taceous rocks. faulting is uncertain. However, evidence of early The Bosque River (fig. 2) has eroded the Bosque Miocene (mid-Tertiary; table 1) movement exists escarpment from the original fault line to its present along certain faults of the apparently related Mexia position. Recent floodplain and terrace deposits con­ system (fig. 1) southeast of the Balcones fault zone ceal bedrock in most areas where faults occur in the (Weeks, 1945, p. 1736). More recent investigators Brazos and Bosque valleys III). Major faults in (Rogers, 1965; and 1964) suggested that the the Waco area have been located by examining out­ Mexia zone was active during deposition of the Glen crops, well records, and cores. Small faults are com­ Ro:e Limestone and the lower part of the Taylor Marl mon throughout the AVaco area, but faults of large of Cretaceous age (tables 1, 2) and that faulting con­ displacement (idem) occur predominantly in the Bos­ tinued into the Tertiary Period. que Valley north and west of Waco. In Cameron Park The origin of the Balcones fault system is unknown. several small grabens and branching faults are visible However, the distinct parallelism between Balcones in the Austin Chalk exposed in Similar faults faults and the deeply buried Paleozoic Ouachita fold- occur just above the mouth of White Rock Creek. GEOLOGY OF WACO 17

GEOLOGIC STRUCTURE OF WACO

The strike of the rock strata IV) in the IV). Aerial photographs taken before Waco area is approximately degrees east of north western Waco was developed show fault alignments The rocks chp eastward at ten to twenty now concealed by homes and streets. Most of these feet per mile in western Waco, but the eastward dip linear features visible on photographs are definitely to 90 feet per mile (one degree dip) in east­ faults and the remainder apparently are smaller faults ern Waco. Available well and bedrock data in the or joints. eastern section (PI. IV) are insufficient to establish a and jointing are best delineated on aerial detailed structural picture where the bedrock surface photographs where the faults and joints cut outcrop­ is concealed by thick soil developed on the Taylor ping formations composed of alternating thin beds of Marl (table 2). resistant and non-resistant strata such as Austin Chalk'. Waco is located on the Balcones fault zone. The Thus, the highest concentration of photographic align­ approximate western limit of the fault zone is the foot ments on the geologic map I) occurs in the area of the Bosque escarpment along the South Bosque of Austin Chalk outcrop. It is probable that the same River (fig. 2; III). Both up-to-the-east and down- concentration of faults and joints occurs in the Taylor to-the-east faults occur in Waco, but principal dis­ Marl outcrop area II) but the trends are rarely placement is down-to-the-east. The fault which visible on aerial photographs of the thick relatively consists of hundreds of faults ranging from a few inches uniform soft shales and marls of the Taylor Formation. to more than 200 feet in displacement, greatly compli­ In summary, the structure of the Waco area is char­ cates bedrock structure. Most major faults occur acterized by complex faulting superimposed on a se- along the Bosque escarpment. of eastward dipping strata. In the Central Faults in the Waco area were mapped by structural Texas area faulting probably occurred throughout most alignments observed on aerial photographs, faults visible of Cretaceous time, and faulting probably extended into in outcrops, interpretation of outcrop patterns, and well early Tertiary time. In the area of Waco, however, it information Major as well as the is impossible to date the faulting precisely. There is general attitude of the rocks in the area, are displayed evidence of displacement along any of the Central on the structural map of the Georgetown Limestone Texas faults since deposition of the oldest Brazos ter­ IV). races during middle Pleistocene time (Quaternary; Outcrop studies and aerial alignments tables 1, 2). Indirect geologic evidence from outside point to other possible faults which correlate remark­ Central Texas suggests that faulting has been inactive ably well with fault trends based on subsurface data since the Miocene (middle Tertiary).

GEOLOGIC STRUCTURE AND WACO DEVELOPMENT

Geologic structure in the Waco area poses no threat size and weight of bridges, over­ to construction or maintenance provided that each de­ passes, and to be a well established trend sign is planned with knowledge of the structural con­ in our civilization. Geological information must, there­ ditions. fore, be part of the essential data on which urban plan­ Until recent construction in Waco was primarily ning is based. based upon the Austin Chalk and Brazos terrace ma­ Large displacement faults in the Waco area bring terials I, II). Foundation problems were few formations of widely varying mechanical properties and failures seldom occurred. For this reason builders into contact along sharp fault lines. Thus it is con­ have largely ignored the underlying geology. Now that ceivable that a foundation mav rest partly upon Austin Waco is growing eastward and westward off the Austin Chalk with a bearing strength of twenty-five tons per outcrop, bedrock geology is becoming a factor that square foot, and partly upon Taylor Marl with a bear­ should not be ignored. ing strength as low as two tons per square foot. Foun­ Structure and stratigraphy are sufficiently complex dations designed for Austin Chalk are inadequate for and varied so that building procedures adopted for one Taylor Marl. Foundations designed for Taylor Marl part of town may almost insure failure in another (figs. are excessively heavy and costly for Austin Chalk. 4, 5, 6). Evidence of this may be observed in various Weathering rates, which depend largely upon degree areas of eastern Waco where wall and foundation de­ of to ground water, air, and biologic activity, signs, which were so successful elsewhere in Waco on are accelerated along fault and joint planes. the Austin Chalk, have failed when constructed on thick soil zones of extent may be develooed different geological material such as the Taylor Marl. in areas where thin soils are normally expected. This Awareness of geological structure is particularly es­ weathering phenomenon may localize failures in foun­ sential where heavy construction is planned, for it is dations and streets, as well as cause accelerated cor­ this type of construction that commonly exceeds the rosion of buried pipes and cables at specific points bearing strengths of the underlying rocks. Increasing where construction crosses a fault or joint. 18 BAYLOR GEOLOGICAL STUDIES

In addition, septic tank fluids may be rapidly con­ ducted along faults or natural "pipes" to surface drain­ Table 1. Geologic time scale. age channels before bacterial and chemical action mod­ ify the sewage sufficiently for surface disposal, result­ ing in a significant pollution hazard. Faults and joints ERA PERIOD may also conduct fluids downward to deeper horizons so that the permeability of an area of bedrock- QUATERNARY may be much greater than expected from examination CENOZOIC of surface rock samples. Joints or faults of even small TERTIARY displacement tend to conduct ground water, which creates drainage problems where faults and joints in­ CRETACEOUS tersect streets, foundations, or excavations. Because faults and joints in the Waco area are es­ MESOZOIC JURASSIC sentially parallel, they have the capacity to act as mechanical wave guides which can direct mechanical TRIASSIC wave energy for considerable distances. Blasting in the fault zone may result in extensive damage to struc­ PERMIAN tures and foundations which occur at considerable dis­ tance along the same fault trend. However, nearby PENNSYLVANIAN structures may not be affected by the blast if they occur at right angles to the fault trend which con­ ducted the maximum mechanical wave energy. Jointing and faulting in the Waco area created nat­ PALEOZOIC DEVONIAN ural north-south planes or partings useful in quarrying. Bedrock excavation by blade in an east-west direction, SILURIAN for example, may be considerably easier than excava­ tion in a north-south direction, particularly in the com­ ORDOVICIAN plexly faulted and jointed area of northwest Waco I, III). CAMBRIAN Although faults and joints may be difficult or im­ possible to detect on the ground, they can commonly be PRECAMBRIAN EON traced on aerial photographs by narrow linear bands of lighter or darker color. For example, drainage lines such as creeks and rivers tend to follow joints and faults. Faults may also be sharply delineated on aerial eastern side, may have lower rates of in­ photographs by distinctively different types of natural creased drawdown, and abnormally high salinities. vegetation which characterizes those formations in fault These water production problems result from fault contact. truncation and displacement of aquifer sands, by de­ Larger faults of the Waco area extend to consider­ creased permeability resulting from increased cementa­ able to the base of the Cretaceous section tion of sands along and near faults, and by contam­ and some possibly into the underlying Ouachita fold- ination of normally fresh water of the Hensel and belt (fig. 3). Water wells situated near large displace­ Hosston sandstones by highly saline Glen Rose water ment faults in the Balcones system, particularly on the which migrates downward along faults and joints.

STRATIGRAPHY

The City of Waco is located on the western edge of H. Beaver, oral communication). Near Waco, wells the East Texas basin and on the eastern edge of the have encountered Paleozoic rocks of the Ouachita stable Texas craton (fig. 1). The Bosque escarpment foldbelt beneath the Cretaceous strata (figs. 1, 3). west of Waco (fig. 2; I) divides the outcrop areas In the following section, geologic formations in the of the Gulfian (Upper Cretaceous) rocks to the east Waco area are discussed as to original definition, age, and the Comanchean (Lower Cretaceous) rocks to the distribution, description, related soils and relation to west. Southeast of Waco near Mart, some wells which urban development. The formations are considered in penetrate the Cretaceous section have bottomed in order of age from youngest to oldest. Formations which evaporite deposits believed to be of Jurassic age (H. are exposed at the surface in the Waco area I, GEOLOGY OF WACO 19

II) are discussed in detail since these outcropping area I, II; figs. 1, 2, 3) is Recent Alluvium, and roclvs have greater effect on city development than the oldest formations are metamorphosed sub-Cre­ do buried formations. In addition, the exposed section taceous rocks assigned to the Ouachita foldbelt. A type is far better understood than the subsurface rocks lithologic and electric log V) for the Waco area beneath Waco. The youngest formation in the Waco is included for the reader's use.

SURFACE FORMATIONS

QUATERNARY SYSTEM

RECENT ALLUVIUM flooding. Flood hazard has been reduced through con­ struction of various flood control and storage reservoirs, BRAZOS ALLUVIUM Qbrf) but the alluvial plains are still to flooding during excessively wet periods. Weatber records for the Brazos and Bosque watersheds are inadequate to per­ CHARACTER AND DISTRIBUTION mit valid of maximum storms. One can Alluvial deposits of the Brazos and Bosque rivers not accurately predict what the maximum storm in a are the youngest deposits in the AVaco area I, hundred or a thousand year period would yield in II). The Brazos River alluvium occupies a more runoff and flood. extensive area than alluvium of the Bosque River. In areas of thick alluvial deposits, a river is not The Brazos floodplain is presently undergoing constrained to occupy the existing channel. During luviation by the deposition of fine-grained sediments. floods the river channel may migrate rapidly through Little or no coarse gravels are being transported meander development or may develop a new channel (Bronaugh, 1950, p. 2). some distance away from the existing channel by de­ The Brazos alluvial belt is narrow where it transects veloping cutoffs. Construction in these alluviated areas the resistant Austin Chalk outcrop in the northern part should be undertaken only if potential loss due to of the Waco area, but as it progresses southeastward, infrequent flooding is acceptable. the belt widens on the less resistant outcropping Taylor Foundation problems in alluvial bottoms of the river Marl (idem). In the easternmost part of the area, are similar to those problems encountered in areas terrace soils are fertile. In this area the Brazos channel of thick soil that is, total support must be has migrated laterally, leaving alluvial deposits in a furnished by the weathered mantle. While there are two miles wide, which extends southward beyond no available data on support values for Brazos River the Waco area. alluvial deposits, it may generally be assumed that Both the Brazos and Bosque river valleys exhibit foundation support values will vary inversely with the floodplain scrolls and meander scars, visible on aerial thickness of the floodplain clay-rich surface materials. photographs as arcuate darker areas on the light-colored Point bar river deposits tend to be well-drained, well- alluvial flats. compacted, sandy loams and sands with low shrink- The alluvial deposits of the Brazos and Bosque values. Meander scars are poorly drained, plastic rivers support a heavy native growth of large deciduous clay and organic-rich loams with higher trees, such as elm, pecan, and oak, and characteristics. Foundation design should take into these trees are visible as mottled, light-colored areas on account the nature of the point bar, aerial photographs. floodplain, or meander scar. Deeper sands and gravel of Brazos River alluvial bottoms provide an excellent source of ground water for limited agricultural or domestic use. Because of the permeability of the deposits, as well as the type The alluvial bottoms are productive farmlands with of land use, all water derived from these shallow sands light sandy loam soils. Soils of the Brazos alluvial will likely be polluted. They should not, therefore, be bottoms grade downward from surficial clay-rich flood- used for human consumption without approved treat­ plain deposits, through bank load quartzose sands, ment. Since the sands are uncemented, well completions into basal siliceous bed load sands and gravels. Areas should involve a designed bottom-hole screen based on of meander scrolls are characterized by thick grain size of the sediment encountered in the well bore. floodplain soils and thinner bank load sands. In general the more productive wells will be located near the present river or in old meander channels RELATION TO URBAN DEVELOPMENT where sands are particularly thick. Before construction of large upstream reservoirs, the A'Vater from these alluvial sands is derived prin­ Brazos River were subjected to frequent cipally from underflow of the river and from bank storage. A small quantity of water for recharge of alluvial sands is derived from drainage of ad'acent terraces and from storm runoff in intermittent streams Soils, water, and economic aspects are con­ sidered in greater detail in other parts of this Urban Geology which discharge onto the alluvial or flow across series. the alluvium to the river. 20 BAYLOR GEOLOGICAL STUDIES

Alluvial sands can normally absorb large amounts of properties of Bosque alluvium are probably more fluid because of the high permeability and porosity. uniform than those of Brazos alluvium. Thickness of Waste water and sewage carrying little or no solids are the alluvium might be determined by refraction seismic readily absorbed by the alluvium. During high water or methods or borehole investigations which would locate wet seasons, however, the water table rises and areas of shallow bedrock. Irregular thicknesses of subsurface drainage is diminished. A waste disposal Bosque alluvium are indicated by bedrock exposures system in alluvial areas should be constructed above along the river channel. the maximum level of the water table. Deeper sands and basal (bed load) gravels of the Brazos River alluvial sands from channel areas and Bosque alluvium should produce small quantities of adjacent floodplain are excellent sources of builder's ground water suitable for limited agricultural and sand. River silt and some plastic clays are suitable for domestic use. This shallow water potential will probably certain ceramic applications. Terrace deposits reworked maintained by normal seepage from Lake Waco. by the Brazos River furnish some commercial gravel. Bosque alluvial water will be polluted by seepage of polluted water from Lake Waco, from septic sewage disposal in Bosque alluvium, and from agricultural fertilizers used on the alluvial plain. Although Bosque BOSQUE ALLUVIUM Qbof) alluvial soils and sediments are normally less perme­ able than those of Brazos River alluvium, Bosque alluvium will transmit properly introduced fluids in CHARACTER AND DISTRIBUTION considerable quantity. The Bosque alluvial sediments are a commercial The alluvial bottoms of the Bosque River I) are source of black topsoil. much narrower, and in the Waco area are exposed only in a small area below dam. Bosque alluvial deposits were derived from the dominantly limestone-clay provenance or source area of outcropping Lower Cretaceous rocks (fig. 1). Some Bosque sediments were derived by erosion of siliceous PLEISTOCENE TERRACES sand and gravel of older (higher) terraces of the Brazos River. The terraces of the Waco area are remnants of older Alluvial valleys of the Bosque River system are river floodplains of Quaternary age left as "steps" by narrow where they transect the Main Street Member of more recent river downcutting I, II). the Georgetown Formation northwest of the map area, and are moderately wide where they cross the Del Rio Clay outcrop. The Bosque River below Waco dam flows in a relatively fixed channel locally entrenched in bedrock TERRACE SYSTEMS except for the last mile of its course before entering the Brazos River. There are two distinct terrace systems in the Waco Other narrow alluvial deposits I, II) occur Brazos system and the Bosque system. The within the city along Waco Creek and south of the city levels of earlier Brazos River alluviation are represented along Cottonwood Creek. by remnants of terraces from 20 to 125 feet above present river level. The earlier Bosque River deposits are represented by terraces 10 to 40 feet above the SOILS present level of the Bosque River mouth. The Bosque alluvium consists of thick clay-rich floodplain soils, bank load clay and sand deposits, and thin bed load limestone gravel deposits. Old bed load clayey limestone gravel deposits, which have been ele­ vated and dissected, are the source of excellent road- building gravels. Floodplain soils have been a com­ mercial source of rich topsoil in the Waco area. Both the and Brazos terrace systems display common depositional characteristics including cross- bedding, contacts with underlying formations, RELATION TO URBAN DEVELOPMENT and carbonate cementation resulting from solution of limestone gravel and precipitation at intergrain bound­ Although it is probable that major flooding in the aries (Bronaugh, 1950, p. 5). lower valley of the Bosque River has been largely eliminated by construction of the new Lake Waco dam, it is still impossible to predict the of simultaneous maximum floods in both the Bosque and Brazos AGE OF TERRACES watersheds. Foundation problems should be anticipated in Bosque Higher terraces of the Brazos River have yielded alluvial bottoms since these deposits contain a higher vetebrate fossils of Pleistocene age. Bosque terraces percentage of plastic clay and thicker clay sections and lower Brazos terraces are of Recent age as de­ when compared with Brazos River alluvium. The termined by archaeological studies (idem, p. 9). GEOLOGY OF WACO 21

BRAZOS TERRACES Brazos terraces constitute the principal source of construction sand and gravel for the Waco area. An estimated 1.2 million cubic yards of gravel were pro­ TERRACE LEVELS duced principally from Brazos terraces during 1964. Reserves within a ten-mile radius of the city are more Brazos River terraces in McLennan County have than adequate to meet anticipated needs for the next 20 been divided into two general a lower terrace years. group varying from 20 to 50 feet above the river, and a higher terrace group varying from 70 to 200 feet above mean low water level (idem, p. 7). For convenience in mapping, four Quaternary BOSQUE TERRACES (Qbot) terrace levels of the Brazos River have been delineated on the basis of elevation above low mean water (1) the lower levels to 50 feet) which com­ CHARACTER AND DISTRIBUTION prise terrace material representing the 20 to 50-foot terraces; (2) the second level to 75 feet) In the Waco area, terraces are primarily west which is the 75-foot terrace; (3) a third level (Qbr3 of Lake Waco I). Commercial deposits of Bosque to 125 feet) which is the 125-foot terrace; and terrace gravels occur west and north of Waco along (4) a fourth level which consists of various tributaries of the Bosque system. terrace material higher than 125 feet above mean low water level. This uppermost level extends northeastward Bosque terraces are composed chiefly of clay and beyond the map area to the vicinity of Elm Mott. limestone gravels deposited by the Bosque rivers which Remnants of Brazos gravels occur intermingled with have cut into Lower Cretaceous shales and limestones Bosque River gravels near the mouth of the North west and north of Waco. Bosque River and in the vicinity of Bosqueville I).

SOILS SOILS

Topsoils on higher Brazos River terraces vary from Soils of the Bosque River terrace system are normally gray to brown and are largely Subsoils calcareous alluvial clays varying from brown to black. are from 5 to 12 inches in depth and are slightly cal­ These soils become lighter colored and increase in careous sandy clay. Lower terrace levels have dark carbonate content with depth. brown soils which vary from slightly calcareous to noncalcareous. Porous have a good water- holding capacity. COMPOSITION

COMPOSITION Bosque River terrace gravels are composed chiefly of limestone pebbles derived from lower of Brazos River terraces are composed largely of sil­ Georgetown Formation and a small amount of chert and iceous sands and gravel (quartz, chert, quartzite) and limestone eroded from the Edwards Formation. minor amounts of reddish clay. Where they are in contact with Austin or Georgetown Limestone, the terraces also contain a large amount of limestone pebbles. RELATION TO URBAN DEVELOPMENT Brazos River terraces commonly support an ex­ tensive growth of deciduous trees and are visible on These gravels are locally consolidated by calcium aerial photographs as light-colored, mottled areas. These carbonate and are capable of supporting substantial terraces form good agricultural soils which are largely foundation loads. The soil cover is commonly thin and in cultivation. easily removed. Bedrock normally occurs only a few feet below the surface.

RELATION TO URBAN DEVELOPMENT Some water is produced from shallow wells in thicker terrace deposits, but the water supply is limited Brazos River terraces, which are composed largely since it is available principally during wet seasons. of sand and gravel, furnish stable, well-drained founda­ Bosque terrace deposits are sufficiently permeable to tion sites for light structures. Bedrock commonly oc­ provide excellent subsurface disposal of small quantities curs at shallow depths beneath the higher level terraces. of treated waste water. High permeability of Brazos terraces makes them Limestone gravel in the Bosque terraces is grade A ideal for disposal of waste water. Terraces of con­ base material for street and highway construction be­ siderable areal extent near the river store limited cause of the abundant clay binder. Much of the Bosque quantities of ground water suitable for domestic use terrace material in the vicinity lies below the after treatment for bacterial pollution. The high perme­ conservation level of Lake Waco. The gravel cannot be ability of these terrace sands almost insures that septic exploited since dredging the gravel from beneath the sewage will find its way into any nearby well. As the water results in loss of the essential calcareous clay area of a given terrace decreases, the storage capacity binder. Limited deposits above lake level occur at also decreases, so that only larger terrace areas furnish localities along North and Middle Bosque rivers, Hog a dependable but limited water supply. Creek, and Harris Creek. 22 BAYLOR GEOLOGICAL STUDIES

CRETACEOUS SYSTEM

Formations of Cretaceous age occur at the surface it is now exposed chiefly in the region east of the (figs. 1, 2) and in the suhsurface (fig. 3; V) of Brazos River. the Greater Waco area. The entire Cretaceous section Normally the Taylor Marl is in unconformable con­ in the Waco area is composed of sedimentary rocks of tact with the underlying Austin Chalk, but the Taylor marine origin. These Cretaceous rocks have been di­ is in fault contact with the Austin Chalk in the area of vided into an upper section of age and a lower Waco Creek and Street (Pace, 1921, p. 17), on section of Comanchean age (table 2; I, II). the Baylor campus, and along White Rock Creek In the Waco area, the Gulfian Series (table 2) from northeast of Steinbeck Bend of the Brazos River. top to base is composed of Taylor Marl, Austin Chalk, Throughout much of its length, this fault contact is South Shale, Lake Waco Formation, and concealed by overlying Brazos River terraces. Five Pepper Shale. These Gulfian rocks, which are 890 feet miles north of Waco along a major fault of the Balcones thick in the J. L. Myers & Sons No. 1 Tiery well system, the Lower Taylor Marl Member is in fault con­ Appendix are exposed at the surface in the tact with the South Bosque Shale of the Eagle Ford Waco area and dip eastward (fig. 3) into the subsur­ Group. face of the East Texas basin. Gulfian rocks in Greater Waco crop out I, II) east of the eastern shore of Lake Waco. Approximately 1700 feet of Comanchean DESCRIPTION Series strata occur below Greater Waco V; fig. 3), but only the uppermost formations (Buda and Del Rio The Lower Taylor Marl Member is a fine-grained, formations) crop out locally in the northwest part of massive, uniformly bedded marl. It is normally gray, the map area 1). but weathers buff and grades rapidly to the dark, rich soil of the Texas Blacklands. Where erosion has stripped the soil cover, the buff-weathering marl forms TAYLOR MARL conspicuous scars on hillsides. Clay minerals, chiefly montmorillonit.e and illite (Beall, 1964, pp. 16-19) com­ pose approximately 60 to 70 percent of the member. ORIGINAL DEFINITION The remaining 30 to 40 percent is composed principally of calcium carbonate, a cementing agent, and minor In 1889, Hill (p. xiii) first called the Taylor Marl amounts of silt, calcite, glauconite, calcium phosphate, the "Blue Blufiis division" for exposures along the hematite and pyrite {idem, p. 16). Colorado River four miles east of Austin. The term Beall (1964, pp. 22-25) concluded that the composi­ 'Taylor Marl" was later applied 1892, p. 73) to tion and uniformity of the Lower Taylor Marl in­ exposures near the town of Taylor. dicate that it was deposited on a broad flat subsiding shelf. Rates of subsidence and deposition were ap­ proximately equivalent. The areal uniformity and the great thickness of the member suggested to Beall a AGE AND DISTRIBUTION long period of deposition in a relatively nearshore shallow marine environment. Marine conditions are The Taylor Marl is middle Gulfian in age (Stephen- indicated by foraminifers, ammonites, clams, scapho- son et 1942, Chart 9). Exposures occur northeast­ pods, and marine vertebrates {idem, p. 23). ward from the Rio Grande embayment to the Red River. The Lower Taylor Marl is principally clastic, varying The formation thins northeastward and southeastward in particle size from clay to silt but containing some from Waco. The Taylor Marl is feet thick in the sand. Sand content increases upward within the mem­ J. L. Myers & Sons No. 1 Pardo well (Appendix I). ber, indicating marine regression in the latter stages of The Taylor Marl unconformably overlies Austin Lower Taylor Marl deposition. The culmination or Chalk and unconformably underlies the Navarro Group climax of sand deposition is represented by the over­ (table 2) in western Limestone County (Stephenson, lying Wolfe City Sand Member. The abundance of 1929, p. 1328). calcium carbonate in the Lower Taylor Marl In Central Texas the formation is divided into four suggests slow clastic deposition relative to biochemical members (table 2). In descending order the members precipitation of calcium carbonate. Oscillation of the are Upper Taylor Marl, Pecan Gap Chalk, Wolfe City strandline as well as climatic changes are possible causes Sand, and Lower Taylor Marl. The Upper and Lower for local variations in silt-clay and clay-carbonate ratios. Taylor Marl members are informally named units in Weathering alters the blue gray color of the Lower this area. (1964, pp. 10-11) modified this class­ Taylor Marl Member to light gray or tan. The marl ification. Only the Lower Taylor Marl Member is ex­ becomes highly fissile where the calcium carbonate ce­ posed in the Waco area I, II). In the J. L. Myers ment is leached. Some weathered marl samples display & Sons No. 1 Tiery well, the Lower Taylor Marl is limonite stains which appear to be the alteration product approximately 230 feet thick. The overlying members of pyrite, the pigmenting material of the unweathered of the Taylor Formation crop out in eastern McLennan marl. County and western Limestone County. Drainage in the Lower Taylor Marl outcrop area is The lithology (marine shale and marl) of the Lower dendritic, due to the relatively homogeneous composi­ Taylor Marl Member indicates that it once covered all tion of the member, but fault or joint control of drainage of the area and extended some distance westward. is suggested by the northeast-southwest of The Taylor Marl has been eroded from most of the segments of Tehuacana, Tradinghouse and Williams area west of the alluvial valley of the Brazos River and creeks II). GEOLOGY OF WACO 23

SOILS Taylor Marl does not produce water because it is relatively impermeable and, therefore, water systems Soils derived from the Taylor Formation are dark, in areas of Taylor outcrop must depend on other plastic "black waxy" soils of the Prairie. sources. Low permeability, however, enables Taylor They are deep dark-gray to black, calcareous, and clay and soil to hold surface therefore, effective crumbly soils. Parent materials are montmorillonitic surface storage ponds may be constructed along the clays, marls and minor amounts of silt-sized quartz. Lower Taylor Marl outcrop. Noticeable swelling occurs in the wet montmorillonite The low permeability of lower Taylor Marl Member clays at the upper surface of the A soil zone. Swelling also limits the water available for deep rooted plants of wet clays reduces surface drying and, therefore, the natural vegetation of the outcrop duces a thin brittle crust over an open spongy soil. area consists largely of grasses and shallow rooted, low Shrinkage cracks extend several feet into the soil transpiration plants. Deep rooted trees can thrive where file following long periods of drought. permeability is increased to a considerable depth by artificial means. Over a significant part of the Lower Taylor Marl outcrop occur thin patches of Quaternary gravel and RELATION TO URBAN DEVELOPMENT sand terraces II). Such areas are characterized by reddish soil (in contrast to typical dark gray soils on Some structures built on soils derived from the lower Taylor Marl) and natural vegetation consists of post part of the Lower Taylor Marl Member have subsided oak and other higher transpiration plants. Even in and shifted laterally. Unweathered Taylor Marl will small areas where gravel veneers (terraces) are but a support up to ten tons per square foot. To obtain max­ few feet thick, foundation and drainage properties re­ imum support, pilings or footings should extend well semble those of the larger, thicker gravel terraces, below the weathered zone. Unweathered Taylor Marl rather than those of the underlying Taylor Marl. For is blocky blue-gray clay, readily distinguished from the example, on these thin terrace deposits light construc­ more friable buff-colored weathered material. In highly tion is using foundations which would prob­ bentonitic zones, marl may yield under loads much ably fail on Taylor Marl. Also, effective septic sewage lower than those noted in short term tests. Weathered disposal is possible in these thin gravel terraces. Taylor Marl and Taylor soils have particularly low Complex faulting and jointing, evident in the Austin yield points. Chalk outcrop area, are not apparent in the Taylor Foundation failures are common in areas underlain Marl, although aerial photographs and electric well by Taylor Marl, largely because adequate footings are logs of the Taylor Marl indicate that jointing and fault­ not provided and/or they do not extend into un­ ing occur. Since soils are normally thicker along faults weathered marl. Because of bentonitic beds in the and joints, the local thickness of the weathered zone Taylor Marl, excavations for piers and footings should above the Taylor Marl cannot be established by a be filled quickly before these highly clays are single exploratory boring, but the depth should be de­ altered through exposure to water and atmosphere. termined by closely spaced holes. High ratios characteristic of bentonitic clays cause flexing of the surface soils with changing moisture conditions. Soil movement resulting from shrink-swell may be several inches, and pressures de­ veloped are sufficient to crack grade-beams and mono­ AUSTIN CHALK lithic slabs. When these clays are in contact with buried struc­ ORIGINAL DEFINITION tures such as septic tanks, storage tanks, or bomb shel­ ters, improper drainage may result in clay expansion The name "Austin limestone" was first used in 1860 which can crush or rupture a structure. This crushing by B. F. Shumard (Wilmarth, p. 93) for ex­ phenomenon is compounded when the buried structure posures near Austin, Texas. is covered by clay back-fill derived from the Taylor Marl. Such damage may be prevented by proper drainage and isolation of the structure from the sur­ AGE AND DISTRIBUTION rounding clay by back-filling with gravel. Loosely compacted Taylor Marl fill is highly plastic The Austin Chalk is of Gulfian age (Stephenson and prone to slump when wet, even on very low angle et 1942, Chart 9) and it crops out in a belt four to slopes. If Taylor Marl is adequately compacted and five miles wide from Sherman to San Antonio and stabilized, it will support low embankments and reason­ thence westward. Because of erosion, the ably heavy loads. Austin Chalk thins southward through the Waco area. The low permeability of the Taylor Marl and the The formation is exposed along the crest and dipslope high proportion of bentonitic clays cause the marl to of the Bosque escarpment (fig. 2; I) in the western swell on wetted surfaces and to resist fluid in­ part of Waco. Along South Fifth Street II) filtration. Thus, septic sewage disposal in areas of neath thin Brazos River terrace deposits, the Austin Taylor Marl outcrop requires large drainage fields. Chalk is in fault contact with the Lower Taylor Marl During rainy weather sewage may find its way to the Member of the Taylor Formation. North of Waco the surface when the drainage field becomes saturated. chalk is exposed along the Brazos River and Where population density is high and septic systems Rock Creek (idem). Quaternary terraces and alluvium are used, Taylor soils will probablv become contam­ of the and Brazos rivers overlie the Austin inated during excessively wet periods. Chalk along most of the river valleys. Along the steep 24 BAYLOR GEOLOGICAL STUDIES face of the Bosque escarpment I) a few feet to Bosque Formation (Seewald, K. O., oral communica­ more than 100 feet of the lowermost part of the Austin tion, 1965). Chalk are exposed. The lower half (120 feet) of the A phosphatic conglomerate also occurs at the base of Austin Chalk crops out at Lover's Leap in Cameron the overlying Lower Taylor Marl. Fossil evidence sug­ Park {idem). The Austin Formation penetrated by the gests that the upper part (250 feet) of the Austin J. L. Myers & Sons No. 1 Tiery in eastern Waco is Chalk in the Dallas area is younger than any of the about feet thick. Austin Formation near Waco. The Austin-Taylor unconformity in the Waco area may represent local erosion of many feet of Austin Chalk prior to deposition of the Lower Taylor Marl Member (Stephenson, 1937, DESCRIPTION pp. 137-138). The Austin Chalk thickens northward by adding The Austin Chalk is composed of alternating beds beds at the top of the formation. The lateral continuity of resistant white chalk and less resistant blue-gray of these individual beds, which is well displayed on Individual beds are rarely more than two feet electrical logs, indicates that the beds may have ex­ thick. Bentonite seams commonly occur in the marl tended southward beyond the present terminus prior layers. A thicker bentonite-rich marl zone, which oc­ to erosion. curs 50 feet above the base of the formation, is readily The composition and faunal content of the Austin distinguishable on electrical logs and in outcrop sections. Chalk indicate that deposition took place in a warm The distinctive alternation of chalk and marl beds is shallow marine environment, principally by biochem­ one of the most characteristic features of the Austin ical precipitation of calcium carbonate. Cyclic variation Formation. The apparent uniformity or similarity of in the sedimentary environment is indicated by the al­ alternating beds makes stratigraphic correlation within ternation of chalky limestone and marl beds. Argillace­ the Austin difficult on the outcrop. Electrical log cor­ ous material (clay minerals) in the Austin Formation relations within the Austin Chalk, however, are precise was probably land-derived and calcium carbonate pre­ because of the lateral uniformity of distinctive electrical cipitation resulted from marine biotic activity. Al­ "kicks" within the formation. though the cause of this alternation in deposition of Balcones faulting complicates correlation of surface chalk and marl is not understood, it may have resulted sections. Evidences of faulting include calcite veins with from climatic variation rather than fluctuation of the slickensided surfaces, offset beds, and Sev­ strandline. Accordingly, the chalk perhaps were eral sets of slickensided surfaces along faults indicate deposited during extended warm dry periods and the recurrent movement. marl layers during wetter and cooler climatic periods. Faults are particularly evident on the outcrop (and on aerial photographs) by offset alternating and SOILS chalk beds of the Austin Formation. Thicker soil de­ velopment along permeable fault and joint zones ap­ pears as darker lines on aerial photographs of the Soils derived from the Austin Chalk are normally Austin outcrop. plastic to granular, highly calcareous with permeable subsoils commonly containing chalk fragments. Brown The chalk layers in the formation average 85 per­ to dark-brown soils are common when the soil zone is cent calcium carbonate, principally microcrystalline cal­ from 12 to 18 inches deep. Thicker soils in poorly cite with minor amounts of foraminiferal tests. The drained areas are dark-gray to black with a crumbly chalky limestones contain minor amounts of silica, iron, surface and less permeable substratum. aluminum, and magnesium in the form of clay minerals. The less resistant blue-gray marls, which contain less calcium, have a higher clay mineral content reflected by RELATION TO URBAN DEVELOPMENT higher silica and iron oxides reported in chemical analyses. All beds within the Austin Chalk contain abundant pelecypods, foraminifers and unidentifiable The support strength of Austin Chalk ranges from fossil debris. Nodules and irregular masses of pyrite 14 to 25 tons per square foot in areas where normal are commonly present in surface sections. chalk and marl layers crop out, but engineering strengths may be much lower on the outcrop of the Chalk beds in the Austin Formation weather buff to few thin clay-rich zones in the lower 50 feet of the white through oxidation of iron compounds (principally formation. Few foundation failures can be attributed disseminated pyrite). Below the weathered zone the to failure of the Austin Chalk. Principal foundation chalk is blue-gray. Marl beds are commonly gray to problems originate in structures which rest upon thin dull blue where clay mineral content is high and buff plastic clays in the formation, or more commonly to dull gray where it is low. where a structure rests upon soil rather than bedrock. The Austin Chalk is more resistant to weathering and Soils on the Austin Chalk, particularly in topo­ erosion than any other formation in the Waco area. graphically high, well-drained areas, are normally so The formation underlies the prominent White Rock thin that they are completely removed in preparation Prairie. Bluffs with protruding resistant chalk ledges for foundation construction. However, in low poorly and receding soft marl beds typify the steep-walled drained areas and where Quaternary channel deposits valleys dissected into the prairie. rest on the Austin Chalk, such thick soils may accumu­ The Austin Chalk is unconformably overlain by the late that excavations may fail to reach fresh bedrock. Taylor Marl, and the chalk rests unconformably upon Austin Chalk soils are particularly plastic, and exhibit the South Bosque Shale. The basal Austin unconformity high ratios. In areas with thick soils, it is marked by a phosphatic conglomerate which con­ is particularly important that foundations extend to bed­ tains abundant fossil material reworked from the South rock deep excavations or by the use of piers. GEOLOGY OF WACO

Austin soils rarely cause foundation problems because scarp face, drainage is accelerated and it is effective the normally shallow soils are removed during founda­ even during wet periods, although pollution may be tion construction. However, in areas of thick soil ac­ increased downslope from the drain. cumulation, high shrink-svvell properties will almost in­ Drains into the thicker marl beds encounter prob­ sure foundation failure if structures are supported by lems similar to those faced when drains are installed in rather than bedrock. the Taylor Marl. Upon saturation the bentonitic clays Faulting and jointing in the Austin Chalk outcrop of the marl tend to seal the drainage ways and filtnjjion area lead to local abrupt changes in thickness. is drastically reduced. Soils of the Austin Chalk ef­ Thick soils are commonly developed along fault or fectively swell when wet, preventing and al­ planes. Also, soils developed on marl beds are normally most precluding successful operation of septic sewage thicker than soils on adjacent chalk beds. disposal systems above Austin bedrock. Along steep banks and bluffs where Austin Chalk Fractured zones in the Austin Chalk may readily and the underlying South Bosque Shale are exposed, accept fluid and may conduct it like pipelines. Excava­ major foundation problems can anticipated. If shale tions encountering joints and faults often develop serious slopes are over-steepened by excavation, gravity slump­ drainage problems, since water inflow along joints may ing of the incompetent shale will occur. Failure of the exceed water loss through filtration into the chalk. steepened shale slopes removes support from beneath Water from septic sewage systems may be conducted the chalk, resulting in failure and slumping of Austin through these natural drains directly to the surface as Chalk blocks. Particular care must be exercised in highly polluted runoff. order to maintain a natural slope angle along hillsides The Austin Chalk probably provides fewer problems and escarpment faces if present structures are to be related to foundations and septic disposal systems and protected. more problems in excavation than any other formation Excavation in the Austin Chalk is more difficult than in the area. A principal factor in the growth of in any other formation exposed in the Waco area. the city has been the presence of this excellent founda­ However, the friable nature of the chalk permits ex­ tion under a major part of Waco. Rock, not soil de­ cavation by mechanical means, since it is possible to use veloped from rock, is essential for adequate foundations heavy crawler tractors or powerful excavators. For and drainage. Recognition of this fact would have pre­ small excavations such as home air hammers vented some of the foundation failures which have oc­ or blasting may be required. Openings in the Austin curred in Waco. Chalk do not require internal support during excava­ tion because of the structural competence of the forma­ tion. The tendency of weathered marls to spall causes SOUTH BOSQUE SHALE banks to cave following prolonged exposure. Exposed banks of Austin Chalk should be sloped or should be capped by a properly anchored surface seal. Unsup­ ORIGINAL DEFINITION ported excavation walls parallel to prominent north- south trending fractures are particularly prone to fail along joint or fault planes. This weakness along joint Rocks of the Eagle Ford Group underlie the Austin and fault planes permits easier excavation by blade or Chalk. The Eagle Ford Group, which was named by ripper where the direction of force is applied at right in 1887 (p. 298) for exposures near Eagle Ford, angles to the dominant north-south fracture system. Texas, is of early age (Stephenson et 1942, Fault and joint systems in the Austin Chalk may Chart 9). The group crops out from the Red River to further complicate construction by serving as effective the Rio Grande. In the Waco area the Eagle Ford mechanical wave guides, and conducting seismic Group is divided into two formations (table 2), the energy for considerable distances. For example, blast­ South Bosque Shale and the underlying Lake Waco ing in the chalk may result in damage to structures a Formation. Both formations are composed dominantly considerable distance from the shot point in directions of dark bentonitic shales, but each has distinctive parallel to fracture systems, but little or no damage characteristics. may occur to nearby structures at right angles to the The South Bosque Shale (Prather, 1902) was re­ fracture system. vived by Adkins and Lozo (1951, p. 118-120) for ex­ The Austin Chalk does not normally produce suf­ posures in Cloice Branch at the community of South ficient water for even modest domestic needs, but Bosque, two miles southwest of Greater Waco. minor quantities of water have been produced from some wells in the chalk. Streams on the chalk outcrop may flow for days or weeks following a wet period, DISTRIBUTION but the water supply declines rapidly during dry periods. The great extent of the outcropping Austin Chalk The South Bosque Shale is exposed along the face of in the city, coupled with the great amount of septic the Bosque escarpment (fig. 2). Along the escarpment effluent released in the area, insure that water produced in the Waco area (PL I), the shale outcrop supports a from the formation is highly polluted. belt of rolling hills below the Austin Chalk caprock Fluid infiltration in the Austin Chalk varies with and above an intermediate topographic bench developed topography and the local lithologic character of the on the resistant upper flagstone (limestone) section of formation. Drains excavated in chalk beds and properly the Lake Waco Formation. This topographic bench bedded in washed gravel will normally dispose of rea­ extends from State Highway 6 {idem) southwest to sonable of fluid. An adequate drainage Moody. The South Bosque Shale thickens eastward in for a private residence in such an area can be installed the subsurface to 160 feet in the J. L. Myers & Sons on to 125-foot lot. When an installation is located No. 1 Tiery well V) ; thickening continues east­ near a topographic depression, such as a valley or ward into the East Texas basin. 26 BAYLOR GEOLOGICAL STUDIES GEOLOGY OF WACO 27

EAST

(1) Alluvium; (2) Taylor (3) Austin (6) Walnut (7) Glen Rose Limestone; (8) Hensel (4) Waco, and Del Rio shales; Sandstone; (9) Formation and Limestone; (10) (5) Georgetown, Edwards and Peak limestones; Hosston Sandstone; and (11) Pre-Cretaceous Ouachita Foldbelt.

Fig. 3. Diagrammatic east-west cross section, Waco area.

DESCRIPTION The formation contains abundant poorly preserved RELATION TO URBAN DEVELOPMENT Foundation loads placed on the unstable South Bosque small ammonites (prominent in the upper 30 to SO Shale should be supported by piers or The South Bosque Formation is dark gray to blaclv, feet), pelecypods, and foraminifers. Some fish teeth and The upper noncalcareous clay of the South Bosque footings extending deep enough so that they rest in soft, blocky, homogeneous shale which weathers vertebrae are also present. Abundant fossils (nektonic), Shale is raw material for expanded aggregate produced unweathered shale. The bases of piers and footings gray to tan. The shale, which is very incompetent, low carbonate content, absence of obvious lithologic by the Waco Aggregate Company. The shale is also should be approximately horizontal or slightly inclined commonly slumps throughout the outcrop belt. Out­ variation and bedding, and abundant bituminous ma­ mixed with Austin Chalk for use in manufacturing away from the hill slope. Such foundations transfer the crops are also normally concealed on gentle slopes by terial suggest that this upper portion of the formation cement by the Universal Atlas Cement Company. Both load to more massive sections of the formation. Founda­ debris from the overlying Austin Chalk. Persistent was deposited in a neritic marine environment with plants are located in the South Bosque Community. tion excavations and borings should be filled immediately bentonite seams are less common than in the underlying before surface water expands bentonitic clays. poor bottom current circulation. Absence of coarse The support strength of the South Bosque Shale Lake Waco Formation (Chamness, 1963, p. 29). Water which seeps downward into the shale along land-derived clastic sediment and uniform eastward varies from two to sixteen tons per square foot. This The South Bosque Shale is unconformably separated piers causes the shale to swell. Swelling is particularly thickening indicate a distant northwestward shoreline. variation is related both to stratigraphic position within from the Austin Chalk. The base of the Austin Chalk evident in the non-calcareous part of the South Bosque There is a marked increase in the of bentonite the formation and to the topographic slope of the build­ includes a conglomerate about one foot thick composed seams, disseminated carbonate, and limestone beds in Formation where wet expanding clays flow pla.stically of shark teeth, fish remains, phosphatic nodules, ing site. Noncalcareous shales in the upper part of the upward and outward along the piers. Drying shrinks the lower part of the South Bosque Shale. The lower formation, which are more plastic than calcareous shales glauconite grains in a chalk matrix. Filled borings the clay and the pier settles slightly in the hole. This part of the formation, therefore, reflects different cli­ the lower part, may fail on gentle slopes even without containing phosphatic and glauconitic material extend "mining" apparently continues as long as fresh water matic conditions and greater volcanic activity than the the additional load of man-made structures. downward into the shale (idem. pp. 33-34). The South sediments in the upper part of the South Bosque Shale. can penetrate along pier walls. Settling is uneven and Bosque-Lake Waco contact is gradational. Thin lime­ When used as fill material, the unstable shales of the the result is cracking of slabs, grade beams and super­ The upper, low-carbonate part of the South Bosque upper South Bosque Formation must be stabilized, stone beds interbedded with the shales of the Lake Shale weathers gray-blue, but the lower part of the incumbent structures. These structural problems are compacted, and adequately drained, and gentle slopes Waco Formation decrease in number upward into more formation weathers tan to brown. The ma­ much more acute in uncompacted South Bosque Shale must be maintained to prevent slumping. The slumping homogeneous marl which characterizes the terial is disseminated limonite derived by the altera­ fill where permeability is high, resulting in accelerated problem is particularly acute when shales of the upper Lake Waco Formation. Marked fissility typical of the tion of pyrite, the principal pigment of the fresh dark infiltration of fresh water. part of the South Bosque Formation are terraced. Lake Waco Formation is less common in the South shale. The formation weathers rapidly and Drainage or infiltration through the South Bosque Throughout the outcrop belt where construction oc­ Bosque Shale which is blocky in the upper part. offers little resistance to erosion. Shale is retarded by swelling clays. When these clays The upper 30 to 50 feet of the South Bosque Shale curs, improper drainage, cut and fill modification of contact fresh water, they swell and effectively seal are composed of dark noncalcareous bentonitic shale slope, superincumbent weight of added topsoil and against additional infiltration. Extremely large in­ beds which are plastic and tend to slump when wet. structures, and constant saturation by watering combine filtration fields are required for effective septic sewage Low carbonate content (2-8 percent) contributes to the SOILS to increase instability. disposal. A lot on the South Bosque Forma­ highly plastic behavior of the upper part of the South Soils developed on the South Bosque Formation Construction in the outcrop area, especially along the tion is probably inadeciuate for the construction of a Bosque Shale. The lower part of the formation is com­ are gray to gray-brown, highly calcareous, and of Bosque escarpment, should maintain the natural slope. septic field for the average home. During dry seasons posed of calcareous shales (30-35 percent) interbedded variable depth, depending upon the slope of the land. This factor is particularly important along the edge of high shrink-swell clays will crack and "fluff" to depths with limestone flags and bentonite seams. The South Bosque soils form rich agricultural lands, but the escarpments where the Austin Chalk is thin. of several feet and drainage will temporarily be ade­ transition from low carbonate to high carbonate clays they are extremely plastic and have high bility on slopes of the upper part of the South Bosque quate, but during extended wet periods infiltration is occurs vertically in a few feet. ratios. Shale (induced by oversteepening through injudicious vastly reduced by clay expansion and septic overflow excavation) causes failure in formerly stable overlying will find its way to the surface in yards and streets to Austin Chalk. surface the South Bosque Shale is 28 BAYLOR GEOLOGICAL STUDIES exposed along the face of the Bosque escarpment, est bench-forming limestone bed. The Bouldin Member drainage polluted with sewage eventually finds its way is approximately 14 feet thick in the Waco area into Lake Waco to become part of Waco's water (Chamness, 1963, VII). The Cloice-Bouldin con­ supply. tact, which is also gradational, is difficult to delineate and map. In general, the lower part of the South Bosque Shale provides a more stable foundation than the upper part. The Cloice Member is a highly bentonitic, calcare­ Greater stability in the lower part results from higher ous, extremely fissile gray shale containing bentonite natural calcium carbonate content (stabilizer) and thin seams up to 14 inches thick. Bentonite beds, however, limestone beds. Support strengths on the formation occur throughout the Lake Waco Formation. The Clo­ vary with stratigraphic and topographic position. ice Member also includes a number of thin limestone beds from one-fourth to two inches thick, intercalated Drainage or infiltration problems in the lower part of with bentonite and shale beds. The member weathers the South Bosque Shale, which has a higher calcium rapidly to pale tan and forms deep rich soils. The Clo­ carbonate content, are similar but less severe than ice Member is approximately 35 feet thick in the Waco those in the upper part of the formation. area (Chamness, 1963, VII). Excavation in the South Bosque Shale is easily ac­ The Bluebonnet Member is composed of interbedded complished by any excavation machine. Thin limestone highly calcareous, bentonitic, fissile shales and hard beds in the lower part of the formation may pose minor fossiliferous limestone flags. The upper two-thirds of excavation problems, but the beds are easily broken. the member is predominately shale. Bentonite beds Excavation walls are subject to slumping, particularly range less than one inch to ten inches lime­ when wet. Deep excavations with unsupported walls stone beds are also one to ten inches thick. The member may be quite hazardous. is dark gray-blue and weathers gray to light The Bluebonnet Member ranges from six to twelve feet thick in the Waco area (Silver, 1963, pp. 42-43). LAKE WACO FORMATION The basal limestone bed of the Bluebonnet Member rests unconformably on noncalcareous, highly plastic ORIGINAL DEFINITION Shale. The Pepper-Bluebonnet contact marks a distinct change in lithology. A thin reworked con­ The Lake Waco Formation was named by Adkins glomeratic zone occurs at the contact in the basal Blue­ and Lozo (1951, p. 120) for exposures in the spillway bonnet limestone flags. Unweathered samples of Blue­ of the Lake Waco Dam. bonnet shale in contact with dilute hydro­ chloric acid, but noncalcareous Pepper Shale will not react to acid. DISTRIBUTION The Lake Waco Formation contains principally montmorillonitic clays with considerable disseminated calcium carbonate, numerous limestone beds, minor The Lake Waco Formation crops out along the Bos­ seams of bentonite, and rare kaolinitic clays and quartz que escarpment from Moody to Lake Waco (fig. 2; sand. The Bouldin and Bluebonnet members contain I) and in scattered outcrops northward along the more than 50 percent calcium carbonate represented by Brazos River. The formation, which is approximately limestone beds and disseminated the Cloice 80 feet thick near Moody, thickens eastward into the Member is less calcareous. East Texas basin. Silver (1963) presented substantial evidence to sug­ gest that the Bluebonnet limestone flags originated in a lagoonal environment, which was modified by slow DESCRIPTION marine transgression during Cloice deposition. Fauna and sedimentary structures suggest that the Cloice en­ The Lake Waco Formation is composed of calcare­ vironment was also restricted, although deeper water ous bentonitic shales interbedded with thin dense lime­ and less agitation are indicated by more uniformly dis­ stone beds. The formation, which is dark gray-blue, tributed sediments in the Cloice Member. Rocks of the varies from to tan on weathered surfaces. The Bouldin Member are similar to those in the Bluebonnet Lake Waco Formation is more calcareous, fissile, and Member. resistant to erosion than is the overlying South Bosque Sedimentary evidence, therefore, suggests that the Shale. Lower "steps" of the Bosque escarpment (fig. Bouldin and Bluebonnet members accumvdated in rel­ 2) are supported by thin limestone beds ("flag sec­ atively similar environments, and that the lower South tions") near the top and base of the Lake Waco For­ Bosque Shale and the Cloice Member of the Lake mation. Waco Formation were deposited under condi­ The Lake Waco Formation (table 2) has been di­ tions. Two depositional cycles can be recognized in the vided in descending order into the Bouldin, Cloice Eagle Ford Bluebonnet-Cloice cycle nnd a and Bluebonnet members (Adkins and Lozo, pp. South Bosque cycle. The upper Bouldin- 120-123). South Bosque cycle grades upward into more The Bouldin Member is composed of highly ben­ marine upper South Bosque Shale. tonitic calcareous shales interbedded with limestone Bentonite seams throughout the Lake Waco Forma­ flags from one-fourth to six inches thick. The Bouldin tion are marine deposits composed of altered volcanic Member of the Lake Waco Formation grades upward ash. The altered ash beds are laterally discontinuous, into the South Bosque Shale, and the contact between apparently because of irregular distribution bv the two units is arbitrarily placed at the top of the high­ currents. Volcanic activity which provided the ash GEOLOGY OF WACO 29 may have occurred along the Balcones fault zone (fig. Since the Lake Waco Formation is normally exposed 1), possibly in the or areas along the face of the Bosque escarpment, much of the 1927, p. 24). contained septic disposal fluid will reach the surface and Streams along the Bosque escarpment (fig. 2) are will vdtimately flow into Lake Waco. commonly incised into Eagle Ford shale sections and in No productive aquifers occur in the Eagle Ford many places streams have cut into the Eagle Ford lime­ Group. Small "wet weather" wells capable of producing stone flag beds. A drainage pattern reflects the a few gallons to a few tens of gallons of water per day geometry of faults and joints of the Balcones system have reportedly produced from the Bouldin and Blue- (Hayward, 1957, p. 31). bonnet members. However, the water supply for these wells is from surface runoff and infiltration, since such wells cease to produce when cased. Uncased wells may SOILS produce small amounts of water for a few days or weeks following a rainy period. The Lake Waco Formation weathers tan by alteration of disseminated (the principal pigment of the unweathered shale) to limonite which colors the weath­ ered rock material. Soils formed on the Lake Waco Formation are olive or yellow-brown calcareous clays. PEPPER SHALE Upper soil horizons gracle downward into unweathered calcareous clay parent material at a depth of five to twenty inches. Yellow-brown soil occurs in areas of ORIGINAL DEFINITION accelerated erosion along steeper slopes and "steps" of the Bosque escarpment. The Pepper Shale was established by Adkins (1932, pp. 417-422) for exposures of dark pyritiferous shale on a branch of Pepper Creek near Belton. RELATION TO URBAN DEVELOPMENT Throughout the area Pepper Shale rests unconform- Shale beds in the Lake Waco Formation will support on Del Rio Clay or upon the locally discontinuous up to 18 tons per square foot, but bentonitic clay sections Buda Limestone. The Pepper Formation is uncon- will support considerably less weight. In general, support formably overlain by the Lake Waco Formation (Sil­ strengths of the Bluebonnet and Bouldin members, ver, 1963, p. 8). which contain numerous intercolated limestone beds, are far higher than in the Cloice Member. Bentonite beds (up to 14 inches thick) in all three AGE AND DISTRIBUTION members of the Lake Waco Formation may fail under stress. Even limestone beds may fail when underlain by The Pepper Shale is earliest Gulfian (table 2) in bentonite. Since the thickness of critical bentonite beds age (Stephenson et 1942, Chart 9). On the outcrop varies with stratigraphic and geographic position, oc­ the Pepper Formation thins southwestward from 150 currence at a local building site can be determined only feet at the county line to a pinchout by excavation or boring. near Austin. The shale is 60 to 70 feet thick in the sub­ High bentonite beds, bentonitic shales, surface of the Waco area and it can be easily recog­ and soils of the Lake Waco Formation cause problems nized on electrical logs V). North of Waco Pep­ with foundations, excavations, and buried structures. per Shale interfingers with thin sand beds of the upper­ Shrink-swell can be minimized by proper drainage and surface sealing, which insures that clays will remain most Woodbine Sand (Adkins and Lozo, 1951, p. 116). properly hydrated and stabilized. Where thicker ben­ Pepper Shale crops out along the base of the Bosque tonite beds are encountered in foundation excavations, escarpment (fig. 2; I) east of the South Bosque the practice is to remove and replace them with River southwest of Waco. Exposures of unweathered stable fill material. Pepper Shale are rare because the formation rapidly Excavations in the Lake Waco Formation will retain weathers. steep faces in dry weather, but slump failure commonly follows soaking rains. Therefore, excavation in this for­ mation should be sloped well back from the vertical and DESCRIPTION the cut face sealed to control moisture content. Because of the tendency for massive failure, heavy retaining The Pepper Formation is noncalcareous, black, structures are required to maintain steep faces cut into dense, pyritic shale. Weathered Pepper Shale is lighter the Lake Waco Formation. in color than the overlying Lake Waco Formation. Excavation in the Lake Waco Formation is moder­ Selenite crystals glisten on weathered outcrops and ately easy. In limestone flag sections, fractures facilitate yellow jarosite also occurs along most minor joints removal by ripper and blade. Shale sections are readily and as irregular masses on weathered Pepper Shale cut by conventional excavating machinery. surfaces. Selenite and jarosite are weathering products Drainage or infiltration into the Lake Waco Forma­ tion is hindered by relatively impermeable bentonite which do not occur in the unweathered shale. beds, bentonitic clays, and dense limestone beds. There­ Pepper Shale contains about 20 percent montmoril- fore, very large drainage fields are required for sewage lonite, 20-25 percent illite, 20-25 percent kaolinite, disposal, and it is probable that during extremely wet percent quartz and 20-25 percent amorphous material, periods, a normal residential lot will be inadequate for probably silica and oxides of iron and aluminum. an effective septic system. Within the upper 10 to 20 feet of the formation, mont- 30 Table 2. Sequence, classification, description and critical properties

System Series, group, Formation Maximum Aquifer or division or member Thickness properties (feet)

Recent and Alluvium and Sand, silt and Yields potable water in some areas at Pleistocene terraces gravel. shallow depth.

Calcareous marls, Yields some potable Taylor 1170 sandy marls, lenses water from Wolfe City of calcareous sandstone, member in eastern part and chalky limestone. of county at shallow depth. Marly limestone Austin 295 and limy shale Not known to yield water in with some bentonite McLennan County. seams.

Shale with lime­ Yields no water South Bosque 140 stone flags. in McLennan County. Eagle Ford

Yields small amounts Shale with limestone flags of water for do­ Lake Waco 145 and bentonite seams. mestic use in western part of McLennan County. on calcareous shale with in­ Reported to some Pepper 100 jected sandstone potable water in dikes in northern northeastern McLennan part of McLennan County. County.

Hard to chalky Yields no water fossiliferous in McLennan County. Buda 35 limestone.

Washita Group Fossiliferous clay Yields no water Del Rio 85 with occasional lime­ in McLennanCounty. stone beds and sandy streaks.

Georgetown 210 Nodular lime­ Not known to yield Cretaceous stones and marly water in McLennan shales. County.

Limestone, Yields some potable Edwards 45 reef water in north­ material, and western McLennan calcareous siltstone. County.

Nodular limestones Yields no water in Comanche Peak Fredericksburg 130 and fossiliferous McLennan County. clay. Group

Shale with some Yields no water in Walnut 175 limestone and sand McLennan County. stringer:,.

Paluxy 20 Sands with some Yields potable water in north­ snales western McLennan County.

Alternating Yields some water in Glen Rose limestones and McLennan County. shales with some anhydrite. Principal aquifer in western el 75 Fine to coarse McLennan County. Yields large sands with green supplies for municipal, in­ shales. dustrial, and domestic

Cow 75 Limestone and Yields no water in Creek shale. McLennan County.

Hammett 100 Shale with Serie s Yields no water in some limestone and sand. McLennan County. Formatio n rearsal l

Gulfia n 95 Limestone and Yields no water in shale. McLennan County.

Uppe r Principal aquifer in |

Serie s | eastern Fine to coarse County. Yields large Hosston sand with some supplies for municipal and conglomerate and Middl e industrial purposes. Water in

varicolored shale. sands in upper part of forma­ tion in southeastern part of

owe r county may be highly Comanchea n I mineralized. Jurassic Cotton Valley Schuler (?) Sands and Yields no water in Group shales (?). McLennan County.

Pennsyl- Shales and vanian (?) Yields no water in County. of geologic formations, Waco area. 31

Slope stability geology Excavation difficulty Infiltration capacity Foundation support strength

will normally Major source of sand and Moderate to requires support slopes greater than some water for Readily excavated by High ; adequate septic sewage some pier support for without shoring. irrigation. light machinery. disposal on average heavy structures. residential lot. fails when wet in None at may contain Moderate to requires slopes less than marginal economic ceramic Readily excavated by Low ; inadequate some pier support for Excavation requires clays. light machinery. even in periods of heavy structures. continuous shoring. moderate saturation. High; will support slopes Furnishes some low subbase Moderate ; adequate septic High ; requires conventional greater than without material for roads and Difficult to excavate with sewage disposal except in design even for heavy shoring, except near basal raw material for light May require period of prolonged structures. contact. cement. blasting or other breaking. saturation. Very low in upper 40 feet; low in lower 120 feet. Along contact with Austin Raw material for cement, Readily excavated by light Low; disposal Low; requires flotation Chalk, basal Austin Chalk expanded aggregate. machinery. even in periods of support or deep piers, will fail by removal or moderate saturation. particularly in upper part modification of shale of formation. support. Low to moderate. Lower in None at contains Moderately easy excavation Member; higher in thin seams of with light machinery. requires some and Bouldin entire formation richly Limestone beds may Low. pier support for heavy limestone zones. require breaking by structures. auxiliary methods.

Very fails when wet on may provide Very low; requires slopes less than marginal economic Readily excavated by Low. flotation support or deep Excavation requires continuous material for ceramic light machinery. piers. shoring. products.

Discontinuous formation. Too thin in Waco area to None; inadequate thickness. Extremely hard discontinuous Will support heavy affect slope stability except Produces oil in Falls County. limestone. Excavation will Low. foundation loads where on erosion resistant cap. range from very difficult present as bed greater than to moderate. 2 feet thick.Overlies Del Rio Clay with moderate to low Moderately to easily excavated Moderate to requires Moderate to fails None; may provide marginal by light machinery. Discon­ some pier deep plastically when wet, economic tinuous limestone beds may Low. piers in noncalcareous parts particularly in noncalcareous ceramic products. require breaking by auxiliary of formation. middle part. methods.

Will support slopes of greater Produces marginal subgrade Not exposed. Not exposed. than without shoring, material within 5 miles Not exposed. except in middle part. of Waco.

Not in deep Produces high quality exposed. Not exposed. Not exposed. excavation in Waco area. dimension stone, crushed rock within 15 miles of Waco.

None not exposed In Waco Not exposed. area. Nothing economic in Not exposed. Not exposed. Not exposed. 50-mile radius.

not exposed in Waco Not exposed. area. Nothing economic in Not exposed. Not exposed. Not exposed. radius.

Not exposed. may contain marginal Not exposed. Not exposed. Not exposed. glass sand within 50 miles of Waco. has produced attractive Not exposed. rough building stone within Not exposed. Not exposed. Not exposed. 50 miles of submarginal.

Not exposed. None. Not exposed. Not exposed. Not exposed.

Not exposed. None. Not exposed. Not exposed. Not exposed.

Not exposed. None. Not exposed. Not exposed. Not exposed.

Not exposed. Not exposed. Not exposed. Not exposed.

Not exposed. None. See aquifer properties Not exposed. Not exposed. Not exposed. column.

Not exposed. None. Not exposed. Not exposed. Not exposed.

Not exposed. None. Not exposed. Not exposed. Not exposed. 32 GEOLOGICAL STUDIES

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34 BAYLOR GEOLOGICAL STUDIES

morillonite content decreases downward from 50 to 25 by impermeable montmorillonitic clays. Therefore, sep­ a corresponding downward increase from 5 to tic disposal systems on Pepper Shale outcrops are im­ 25 percent illite also occurs, but kaolinite and quartz practical. content display no apparent vertical variation (McAtee Oxidation of pyrite within the shale by near-surface and Johnson, 1963, pp. 2-3). waters yields a highly acid effluent which may kill plants Foraminifers and ammonoid casts, some thick-shelled in the overlying soil. Since the Pepper Shale outcrop is pelecypods, and abundant siderite and pyrite suggest characterized by paucity of vegetation, it can be traced that the Pepper Shale was deposited in a brackish to readily in the field and on aerial photographs. Because marine, nearshore environment. The relatively uniform of highly acid weathering Pepper Shale forms lithology of the Pepper Shale is evidence that the dep- a corrosive environment for buried pipes and other ositional environment was essentially constant, except metal objects. for possible minor salinity and pH-Eh variations. In the Waco area the outcrops of the upper South Minor fluctuations in the depositional environment are Bosque Shale and the Pepper Shale are areas which evidenced by a limestone 27 feet below the present the most difficult foundation, drainage, corrosion top of the formation, a phosphatic nodule bed 5 feet and stability problems. Construction on the outcrop of above the base, and local hematite layers throughout these two shale formations should be designed with full the shale. Hematite layers are probably altered (oxi­ recognition of the complex specific properties and se­ dized) siderite-rich clay zones, which originated under vere limitations displayed by these formations. reducing conditions in the depositional environment.

BUDA LIMESTONE SOILS ORIGINAL DEFINITION Calcareous brown soils, which normally overlie the Pepper Shale, are commonly derived from calcareous All pre-Pepper Shale Cretaceous formations in Cen­ clays transported from the overlying Eagle Ford Group. tral Texas are within the Comanchean Series (table 2). North of Lake Waco, however, where the Pepper The Buda Limestone, Del Rio and George­ Shale interfingers with the Woodbine Sand, Pepper soil town Formation compose the Washita Group (table 2) is brown to gray, sandy, and noncalcareous with a which crops out in the Washita Prairie (fig. 2). mottled clay subsoil of low permeability. This soil is The Buda Limestone, originally called the "Shoal normally covered by Bosque terrace deposits and is Creek Limestone," was named by Vaughan (1900, p. rarely more than a few inches thick where it is commonly 18). At the type locality near Buda in Hays County, exposed on steep slopes. the formation is a yellowish dense limestone overlying Del Rio Clay (Wilmarth, 1938, p. 286).

RELATION TO URBAN DEVELOPMENT AGE AND DISTRIBUTION

Pepper Shale yields plastically under normal loads The Buda Limestone, which is late Comanchean because of the absence of disseminated calcium carbonate, (table 2) in age (Stephenson et 1942, Chart 9), which serves as a binding and stabilizing material crops out from Eagle Pass to Waco. The limestone oc­ in many shales. Maximum support strength of this unit curs in the subsurface east of the Waco outcrop where is very low, although exact figures are not available. it thickens downdip into the East Texas basin. Slumping commonly occurs along steep slopes. Under In the Waco area the Buda Limestone rests conform­ heavy loads or along shear surfaces, the formation fails ably upon Del Rio Clay, and is unconformably over­ plastically. High montmorillonite clay content of the lain by Pepper Shale (Ray, 1964, p. 8). Where Buda Pepper Shale leads to excessive properties Limestone is Pepper Shale rests unconformably which cause failure of slabs and grade beams resting up­ upon Del Rio Clay. on the shale. East of the outcrop the Buda Limestone occurs in The homogeneous nature of the shale precludes the the subsurface throughout most of the area. It is six possibility of locating a satisfactory foundation zone feet thick in the J. L. Myers & Sons No. 1 Tiery well within the formation. Where very heavy structures are V). Buda Limestone crops out in the Waco area to be constructed on the outcrop of the Pepper Shale, as discontinuous beds of blocky limestone from a few foundation piers should be carried through the shale inches to two feet thick, but it has not been recognized into the more stable underlying Del Rio Clay. Highway on the outcrop north of China Springs. On aerial photo­ and street construction in the area of Pepper Shale graphs the formation can be traced as a thin light-col­ outcrop requires adequate drainage, compaction of the ored discontinuous line near the base of the Bosque es­ shale, well-drained base material, and preferably the carpment. use of a flexible paving. Pepper Shale is easily excavated. The shale spalls immediately after exposure to weathering and it soon DESCRIPTION fails by slumping. Excavations should, therefore, have gentle slopes, and shale surfaces should be sealed by an The Buda Limestone in the Waco area is hard, mas­ impervious material. sive, buff to gray, dense bed containing abundant Water is not produced from the Pepper Shale. Drain­ pelecypods. It contains approximately 85 percent calcium age or infiltration within the Pepper Shale is hindered carbonate, grains and pebbles of hematite, some pyrite GEOLOGY OF WACO 35 and siderite. Glauconite is relatively common (Ray, of the Rio Grande. The Del Rio Formation is about 85 1964, p. 16). The formation also contains quartz sand feet thick in the J. L. Myers & Sons No. 1 Tiery Well which increases northward to about 52 percent near V), and it does not thicken significantly eastward China Springs {idem, p.. 11-12). across McLennan County. Abundant calcium carbonate, abundant large thick- The formation crops out on higher divides between shelled pelecypods, some quartz sand, and filled borings eastward flowing tributaries of the Bosque River (fig. suggest that the Buda Limestone was deposited under Exposures of Del Rio Clay are poor, and the outcrop relatively warm, shallow marine conditions. Glauconite is commonly covered by soil. The Del Rio occurs in the outcropping Buda Limestone, as well as rapid beneath Bosque terrace deposits (Qbot) along most downdip thickening, indicates that the updip fades of of the western side of Lake Waco I). the Buda was slowly deposited in a nearshore marine environment. The discontinuous outcrop of the Buda Limestone and the Buda-Pepper unconformity are evi­ dence that at least part of the updip thinning of the DESCRIPTION Buda resulted from pre-Pepper erosion. Sand in the out­ cropping Buda in the Waco area also suggests that part of the updip thinning may have been depositional The Del Rio Formation is blue-gray, blocky clay with { idem). rare thin lenticular beds of highly calcareous siltstone and limestone composed predominantly of pelecypods. The clay is also fossiliferous and contains abvmdant disseminated and concretionary pyrite, some marcasite SOILS and siderite. In the Waco area Del Rio Clay is unconformably Soils of the Buda Limestone are relatively insignifi­ overlain by the Pepper Shale where the Buda Limestone cant in the Waco area since the outcrop is narrow and is absent. The Del Rio Clay grades downward into the discontinuous. Light-colored soils from the Buda can Main Street Member of the Georgetown Formation. be distinguished on aerial photographs. The Del Rio Clay-Georgetown contact approximately coincides with the boundary between the Exogyra zone (Del Rio Clay) and the zone (Georgetown Formation). This faunal RELATION TO URBAN DEVELOPMENT boundary occurs in the uppermost part of the George­ town Limestone in the area. The Buda Formation is so variable in thickness and The Del Rio Clay is approximately 10 percent distribution in the Waco area that its effect on construc­ montmorillonite, 20 percent illite, 20 percent kaolinite, tion and engineering is unpredictable. The limestone 10 percent quartz, 30 percent calcite, and 10 percent is too thin and discontinuous to be of value in supporting amorphous material. Calcite is least abundant near the large heavy structures. It is insufficiently thick to ab­ middle of the formation. sorb significant volumes of infiltrating in addi­ The Del Rio Clay was probably deposited during a tion it occurs between impervious shales. minor marine regression and lower At Satin oil field in northern Falls County, the part of the formation reflects regression and the upper formation is an oil reservoir. Buda Limestone quarried part reflects transgression. The lower regressive phase at Pendleton in Bell County, was used locally in con­ of the Del Rio Clay, which is in transitional contact structing stone fences and older buildings. The stone with the underlying Georgetown Formation, displays is an excellent building material, but it is insufficiently from the base to the middle of the formation an upward thick for commercial exploitation in the Waco region. decrease in calcium carbonate and an increase in sand content and pyrite. In addition, a normal marine fauna at the base of the Del Rio Clay grades upward to oysters and a dwarf pyritized fauna near the middle of DEL RIO CLAY the formation. The upper transgressive phase of the Del Rio Clay exhibits vertical mineralogic and faunal trends which ORIGINAL DEFINITION are the reverse of those observed in the regressive phase. From the middle of the formation upward The Del Rio Clay was named by Hill and Vaughan (transgressive phase), calcium carbonate increases, sand in 1898 (p. 2) for exposures of laminated clay over­ content and pyrite decrease, and a more normal marine lying the Fort Worth Limestone (of the Georgetown fauna appears. Formation) in the Rio Grande Valley near Del Rio, Del Rio Clay weathers from to light gray Texas. or buff as pyrite is oxidized to hematite and hydrated iron oxides. Oxidation of pyrite is accompanied by the production of sulphurous and sulphuric acids, which react with carbonates to form selenite crystals on weath­ AGE AND DISTRIBUTION ered Del Rio outcrops. The Del Rio Clay is easily eroded. The formation is The Del Rio Clay is late Comanchean (table 2) in readily cut by rill wash, and streams are commonly in­ age (Stephenson et ah, 1942, Chart 9). It is exposed trenched in the clay. Minor drainage on the Del Rio along the eastern edge of the AVashita Prairie (fig. 2) Clay displays a dendritic pattern because of the lateral of Central Texas and southward to the Big Bend homogeneity of the clays. 36 BAYLOR GEOLOGICAL STUDIES GEOLOGY OF WACO 37

SOILS RELATION TO URBAN DEVELOPMENT

Soils derived from the Del Rio Clay are dark gray- The Del Rio Formation possesses engineering prop­ brown and highly productive. Del Rio soils are best erties similar to those of the Lower Taylor Marl Mem­ developed in the area immediately northwest of the ber. The Del Rio Clay becomes highly plastic when South Bosque River along the eastern edge of the wet, forms corrosive soils, is relatively impermeable Washita Prairie (fig. 2). A few small isolated out­ to drainage or infiltration, excavates easily, and fails crops of Del Rio Clay occur in the Greater Waco area by slumping and plastic failure on relatively gentle (PL I). slopes. The calcareous sections of Del Rio Clay will support up to a maximum of seven tons per square foot, but the less calcareous sections will fail under much lower and will readily slump on cut faces.

SUBSURFACE FORMATIONS

Rocks older than Del Rio Clay are not exposed at in the vicinity of Greater Waco I, It was the surface in the Greater Waco area. Interpretation of encountered in the excavation for the stilling basin be­ subsurface geology in the Waco area is based upon low the spillway of Lake Waco Dam. The Main Street electrical logs, drillers' logs, well cuttings, core holes, Member crops out along the North Bosque River and and extrapolated outcrop information. Description of along tributaries of the South Bosque River. The Main these formations is abbreviated since only surface prop­ Street Member is 37 feet thick along the Bosque River erties are important to Waco urban development. west of Waco (Dixon, 1955, p. 22). In Greater Waco wells have penetrated about 1700 feet of Comanchean strata (Lower Cretaceous) and have drilled into underlying slightly metamorphosed rocks of Paleozoic age (table 2), which are part of the RELATION TO URBAN DEVELOPMENT Ouachita foldbelt 1961). The Main Street Member, which crops out north and west of Waco, has high support ranging to more than 25 tons per square foot. The member GEORGETOWN FORMATION weathers to thin rocky soils, and in permeability it is similar to Austin Chalk. Excavation is difficult but can be accomplished by ripper and blade. The member ORIGINAL DEFINITION disintegrates under abrasion, and, therefore, is less suit­ The formation was named by Hill for Georgetown in able for road material than Edwards Limestone or ter­ Williamson County, but Vaughan (1900) formalized race gravels, although certain horizons make good sub- base road material. The Main Street Member slakes the term in a report on the Uvalde area. upon weathering, but is capable of maintaining steep excavation faces. AGE AND DISTRIBUTION The physical properties of lower members of the Georgetown vary with the clay/limestone ratio, but The Georgetown Limestone is late Comanchean they are not exposed in the Greater Waco area. The (table 2) in age (Stephenson et 1942, Chart 9). lithology of these members is illustrated on the type The formation crops out from the Rio Grande to Red electrical log V). River (fig. 1). In the Waco area the formation grades into the overlying Del Rio Clay and rests unconformably upon the Edwards Limestone. The Georgetown Formation crops out west of Greater Waco EDWARDS LIMESTONE in the Washita Prairie, which occurs west of the Bosque escarpment (fig. 2). The Fredericksburg Group (table 2) in the Waco area is composed of formations which are, in descend­ ing order, Edwards Limestone, Comanche Peak Lime­ DESCRIPTION stone, Walnut Clay and possibly some thin sand beds of The formation is divided into seven members (table the Paluxy Formation. Rocks of the Fredericksburg 2), which are in descending order: Main Street Lime­ Group, which are mid-Comanchean in age stone, Pawpaw Shale, Weno Limestone, Denton Lime­ et al., 1942, Chart 9), crop out in the dissected Lam- stone. Fort Worth Limestone, Duck Creek Limestone, pasas Cut Plain (fig. 2). rnd Kiamichi Shale. The Edwards Limestone was named by Hill and Only the Main Street Limestone Member is exposed Vaughan in 1898 (p. 2). The original description was 38 BAYLOR GEOLOGICAL STUDIES

based upon exposures in Edwards Plateau of The Walnut Clay is conformably overlain by Coman­ south-central Texas, but the presently accepted type che Peak Limestone, and it rests conformably upon and locality is along Barton Creek near Austin (Adkins, interfingers laterally with the Paluxy Sand. 1932, p. 339). The Edwards Limestone is exposed in a belt trend­ ing northeast-southwest across Central Texas, and in the Edwards Plateau of south-central Texas. PALUXY SAND The Edwards Limestone is exposed west of Waco near Crawford, and westward into the Hill Country The Paluxy Sand was named by Hill in 1891 (p. where it caps the flat-topped hills of the Lampasas Cut 504) for exposures of sand near Paluxy townsite in Plain (fig. 2). Within the Waco area from 20 to 40 Somervell County. In Central Texas the formation is feet of Edwards Limestone occurs in the subsurface the lowest unit of the Fredericksburg Group (Lozo, V). Thickness varies because of reef "build-ups" 1959, p. 18). The Paluxy Sand crops out as a sandy in the patch reef facies of the Edwards Formation oak-covered belt in the Hill Country northwest of (Frost, 1963). Examples of reef structure are visible Waco. along the Middle Bosque River near Crawford. The reef In the northwestern part of Greater Waco the Paluxy facies of the formation furnishes excellent crushing Sand is represented by thin, fine-grained, calcareous stone for road base material and quarry blocks for rip­ sandstone beds below the Walnut Clay and above the rap. Part of the riprap used in construction of Glen Rose Limestone. Sands of the Paluxy Formation Waco Dam and associated structures is Edwards Lime­ grade upward into Walnut Clay and rest stone. Quarries in Edwards Limestone near Oglesby, upon Glen Rose Limestone. Crawford, Valley Mills and Gatesville have supplied Waco occurs at the southeastward pinchout of the abundant building stone. High purity limestone is ob­ Paluxy Sand. South and east of the Waco area, the tained from reef facies of the Edwards Formation in Paluxy Sand is absent. For example, the L. Myers Central Texas. & Sons No. I Tiery well V) occurs immediately The Edwards Formation contains ground water west east of the Paluxy pinchout. Therefore, Walnut Clay of Waco, but it does not yield potable water within the rests directly upon Glen Rose Limestone throughout Greater Waco area. much of the eastern part of Greater Waco. The Paluxy Sand thickens northward and westward from AVaco, where it is an important shallow aquifer. Flowing wells have been completed in Paluxy Sand near China Springs, and the South Bosque oil field has COMANCHE PEAK LIMESTONE produced from Paluxy Sand for 65 years.

The Comanche Peak Formation was named by in 1889 (pp. 14, 17-19) for exposures on Comanche Peak in Hood County. The formation is exposed in GLEN ROSE LIMESTONE the Hill Country or Lampasas Cut Plain (fig. 2) of Central Texas, where it crops out beneath the Edwards The Trinity includes the oldest Cretaceous Limestone on upper steep slopes of the distinctive flat- rocks of the Coastal Plain of Texas. In Central Texas topped hills. the Trinity Group (table 2) consists, in descending The Comanche Peak Limestone is composed of alter­ order, of Glen Rose Limestone, Hensel Sand, Pearsall nating layers of dark gray, nodular, earthy limestone Formation, Formation, and Hosston Sand. and calcareous clay. In the subsurface of the Waco area, Rocks of the Trinity Group in Greater Waco rest it is approximately 150 feet thick V). It is con­ upon pre-Cretaceous slightly metamorphosed rocks formably overlain by Edwards Limestone and rests con­ (figs. 1, 3) assigned to the Ouachita foldbelt formably upon the underlying Clay. 1961). The Glen Rose Limestone was named by in 1891 (pp. 504, 507) for exposures near Glen Rose, Somervell County. The formation is exposed in the Glen Rose Prairie, a limestone outcrop belt between WALNUT CLAY the sandy outcrop belts of the Paluxy and Rose Trinity sand sections. Walnut Clay was first defined by Hill in 1891 (pp. In the Waco area, the Rose Formation is ap­ 504, for yellow clays, coquinoid oyster banks, and proximately 715 feet thick in the J. L. Myers & Sons flaggy limestones overlying the Paluxy Sand near Wal­ No. I Tiery well V), and it is divided into an nut Springs, Bosque County. In Central Texas it is upper and lower Glen Rose Limestone separated by a exposed along valley floors and lower valley walls in massive anhydrite section. In the type well (idem) the the Hill Country or Lampasas Cut Plain (fig. 2). massive anhydrite occurs between the depths of 1970 The Walnut Clay consists principally of an upper feet and 2030 feet. shale unit and a lower unit of coquinoid (oyster) lime­ stones and thin dense limestone beds. The formation is 195 feet thick in the subsurface of the Waco area V). It is the thickest clay unit encountered in ''Aquifer properties of the formations of the Trinity Group of the Waco area are in detail in a later publication drilling the sub-Del Rio rocks of the Waco area. of this series. GEOLOGY OF WACO 39

In a report on the Trinity aquifers of McLennan PEARSALL FORMATION County, Holloway (1961, p. 16) presented the following description of the Glen Rose Limestone in the sub­ The Formation was named by (1944) surface of the Waco area. for a subsurface formation in Frio County. The forma­ tion is composed of two members (table 2), an upper "The upper Rose limestone is tan porous shelly limestone, slightly glauconitic at the top and partly Cow Creek Limestone Member and a lower Hammett oolitic with gray thinly laminated interbedded shales. Shale Member. These two units, recognizable in the Foraminifera are present. East Texas basin, grade northwestward to sand in the The massive anhydrite is white crystalline anhydrite interbedded with tan chalky highly porous limestone vicinity of Waco, and they are difficult to distinguish and gray thinly laminated shale. The anhydrite thins west of Waco. rapidly westward and is rarely encountered in wells of In the Waco area the Pearsall Formation is approxi­ western McLennan the anhydrite drill­ ing fluids in the eastern part of the county. mately 80 feet thick V) and does not produce sig­ The lower Glen Rose limestone is tan porous chalky nificant quantities of water. It is an excellent subsur­ limestone with gray thinly laminated interbedded shale. face marker between Hensel Sand and the underlying The foraminifer is common in this Hosston Formation (Holloway, 1961, p. 16). unit. Hill (1901) and Adkins (1923) reco.gnized water horizons in the Glen Rose limestone. Several wells within the county produce from the Glen Rose lime­ stone, but the water is highly mineralized." FORMATION

The limestone (table 2) was named by Imlay (1940, p. 33) from the Sligo field in northeastern Lou­ HENSEL SAND isiana. The Sligo Formation consists of brown to gray oolitic to crystalline limestone. occurs in the subsur­ face east of Waco, and is approximately 20 feet thick The name Hensel Sand (table 2) was proposed by in the J. L. Myers & Sons No. 1 Tiery water well Hill (1901, pp. 141-144, 152) for outcrops in Burnet V). West of Waco it grades into sand and shale dif­ County. Rose Trinity formations crop out ficult to distinguish from the underlying Hosston sand. in the sandy Western Cross Timbers belt. Holloway (1961, p. 16) described the Hensel Sand in McLennan County. "The Hensel sand member of Hill and of HOSSTON SAND Adkins), within McLennan County, is the first sand encountered in drilling below the basal limestone beds of the Glen Rose Limestone. It is white, fine to coarse­ The Hosston Sand was named by Imlay (1940, p. grained, sub-rounded to sub-angular unconsolidated 29) from wells in northwestern Louisiana. Holloway shales are interbedded in the Hensel sand (1961) described the nature and characteristics, as well member in the western part of the county. as the aquifer properties of the Hosston sand. He Electric logs indicate that the sand thins in the northwest part of the county. The Hensel sand mem­ stated that the Hosston Sand is composed of "fine to ber contains abundant high quality many wells coarse, red to white, porous sand, locally cemented near Waco produce from the sand." with calcite" {idem, p. 16). In the L. Myers & Sons In the western part of the Waco area, a large volume No. I Tiery well V) the Hosston Formation, of artesian water is produced from Hensel Sand, which which is 275 feet thick, is composed of approximately is approximately 70 feet thick (PL V). Wells produc­ feet of aquifer sand. Holloway {idem, p. 16) noted ing from this sand are numerous, and more are drilled that the "Hosston formation is the more productive of each year for public, industrial, and domestic use. the two aquifers of McLennan County. In the In drilling for deep water the first productive eastern part of the county all public and industrial zone encountered in the Waco area will be the Hensel artesian wells produce from this formation. Water Sand. from the Hosston formation is normally good quality."

PRE-CRETACEOUS ROCKS

Rocks older than Cretaceous have been recognized in Deep wells within McLennan County have encoun­ deep wells in the Waco area. These rocks belong to the tered Paleozoic foldbelt rocks composed of dark lime­ folded, faulted, and somewhat metamorphosed strata of stone, feldspathic and quartzose sandstones with calcite the Ouachita foldbelt 1961). Rocks of the and disseminated garnet. Ouachita are predominantly phyllites, slates, In southeastern McLennan County, possible Jurassic metaciuartzites, and schists of Paleozoic age. Foldbelt rocks (table 2) overlie rocks of the Ouachita foldbelt rocks, however, include igneous and sedimentary, as and underlie initial or basal deposits of Cretaceous age. well as metamorphic types. Various degrees of meta- Little is known of the detail structure of pre-Cretaceous morphism have been recognized {idem). rocks of the Waco area. 40 BAYLOR GEOLOGICAL STUDIES

REFERENCES

W. S. (1923) The Geology and mineral resources of Correlation of Lower Cretaceous forma­ McLennan Univ. Texas 2340, 202 pp. tions of the Coastal Plains of Texas, Louisiana, and U. S. Survey, Oil and Gas Prelim. The Mesozoic systems of Texas in The Chart No. 3. geology of Univ. Texas Bull. 3232, pp. JOHNSON, CHARLES (1964) Stratigraphy of the Rio Clay, Lozo, F. E. (1951) Stratigraphy of the Wood­ Central Texas in Shale environments of the Mid-Cretaceous bine and Eagle Ford, Waco area in The Woodbine and section, Central field Baylor Geological adjacent strata of the Waco area of Central Texas: South. Society Publication, pp. 4-12. Meth. Univ. Fondren Sci. Ser. no. 4, pp. 105-164.

ATLEE, WILLIAM A. (1962) The Lower Cretaceous Paluxy LONSDALE, J. T. (1927) Igneous rocks of the Balcones fault Sand in Central Baylor Geological Studies Bull. region of Texas: Univ. Texas Bull. 2744, p. 178. No. 2, 26 pp. Lozo, FRANK E. (1959) Stratigraphic relations of the Edwards ARTHUR O., JR. (1964) Stratigraphy of the Taylor Limestone in Central Univ. Texas Pub. 5905, Formation (Upper Cretaceous), East-Central Texas: Bay­ pp. 1-19. lor Geological Studies Bull. No. 6, 35 pp. MCATEE, JAMES and JOHNSON, CHARLES (1963) X-ray dif­ L. Geology of Brazos River terraces in fraction analyses of shale samples from Waco Open- McLennan County, Unpublished master's thesis, file research report no. 304, Geology Department, Baylor University of Texas. University.

RALPH S. (1963) Stratigraphy of the Eagle Ford PACE, LULA (1921) Geology of McLennan County, Texas: The Group in McLennan County, Unpublished master's Baylor Bulletin, vol. XXIV, no. 1, 30 pp. thesis, Baylor University. PRATHER, J. (1902) A preliminary report on the Austin CONGER, RODGER N. (1945) Highlights of Waco history: Hill Chalk underlying Waco, Texas and the adjoining territory: Printing and Stationery Co., Waco, Texas, pp. 14-38. Trans. Tex. Acad. Sci., vol. 4, pt. II, no. 8, pp. 115-122.

DEUSSEN, ALEXANDER (1924) Geology of the Coastal Plain of RAY, JOHNNY (1964) The Buda Limestone of Central Texas: Texas west of Brazos U. S. Survey Prof. Unpublished senior thesis, Baylor University. Paper 126, 139 pp. RoDGERS, ROBERT W. Stratigraphy of the Glen Rose J. W. Population studies of the brachiopod Limestone of Central Unpublished master's thesis, occurring in the Lower Cretaceous Baylor University. Georgetown Formation of Central Unpublished Ph.D. dissertation, University of Wisconsin. SILVER, B. A. (1963) The Bluebonnet Member, Lake Waco Formation (Upper Cretaceous), Central lagoonal FLAWN, PETER T. (1961) The subsurface Ouachita structural Baylor Geological Studies Bull. No. 4, 46 pp. belt in Texas and southeast Oklahoma in The Ouachita University Texas Pub. 6120, pp. 65-105. Conservation Service (1958) Soil survey, McLennan County, U. S. Department of Agriculture, SCS, FROST, J. G. (1963) The Edwards Limestone in Central Texas: series 1942, no. 17, 124 pp. Unpublished master's thesis, Baylor University. L. W. (1929) Unconformities in the Upper O. T. The structural significance of the Cretaceous Series of Am. Assoc. Petrol. Geol. Bosque escarpment, McLennan County, Unpublished vol. 13, pp. 1323-1334. Ph.D. dissertation, University of Wisconsin. Stratigraphic relations of the Austin, Tay­ E. ROBERT (1962) Water diagenesis in Lower lor, and equivalent formations in U. S. Geol. Survey Cretaceous Trinity aquifers of Central Baylor Prof. Paper pp. 133-146. Geological Studies Bull. No. 3, 38 pp. STEPHENSON, L. W. ct (1942) Correlation of the outcrop­ HILL, R. T. (1887) Topography and geology of the Cross ping Cretaceous formations of the Atlantic and Gulf Coastal Timbers and surrounding regions in northern Am. Plain and Trans-Pecos Geol. Soc. America Bull., Jour. Sci., ser. 3, vol. 33, pp. 291-303. vol. 53, pp. 435-448.

A preliminary annotated check list of the VAUGHAN, T. W. (1900a) Reconnaissance in the Rio Grande Cretaceous invertebrate fossils of Texas Geol. coal field of Texas: U. S. Geol. Survey Bull. 164. Survey Bull. no. 4, 57 pp. Description of the Uvalde quadrangle: The Comanche Series of the Texas- U. S. Geol. Survey geologic atlas, Uvalde folio (no. 64). Arkansas Geol. Soc. Am. Bull., vol. 2, pp. 503-524. WEEKS, A. W. (1945) Balcones, Luling, and Mexia fault zones Taylor or Exogyra Ar­ in Texas: Am. Assoc. Petrol. Geol. Bull., vol. 29, pp. 1733- tesian Investigations, final report, pt. 3, p. 73, U. S. 52nd 1737. Cong., 1st. Sess., S. Ex. Doc. 41. WILMARTH, M. GRACE (1938) Lexicon of geologic names of the Geography and geology of the Black and United States: U. S. Geol. Survey Bull. 896, pt. 1. Grand prairies, Texas: U. S. Geol. Survey, 21st Ann. Rept., pt. 7, 666 pp. Vaughan, T. W. (1898) Description of the Editor's published and unpublished references Nueces U. S. Geol. Survey geologic atlas, are available on Central Texas geology, soils, water, en­ Nueces folio (no. 42), 4 pp. gineering and other aspects. The Baylor Geology Depart­ ment has available for perusal many published and un­ HoLLowAy, HAROLD D. (1961) The Lower Cretaceous Trinity published master's theses related to Central several aquifers, McLennan County, Baylor Geological hundred open-file reports pertaining to Central Texas earth Studies Bull. No. 1, 32 pp. science; and extensive library references, aerial photographs, electric well logs, maps and other pertinent data. The R. W. (1940) Lower Cretaceous on Jurassic forma­ Geology Library contains State and Federal reports, maps, tions of southern Arkansas and their oil and gas pos­ and charts, as well as extensive bibliographic references. sibilities : Ark. Geol. Survey, Circ. no. 12, 64 pp. Citizens are invited to use this source of earth science data. GEOLOGY OF WACO 41

SUMMARY AND CONCLUSIONS

(1) Greater Waco (figs. 1, 2) is located on the ground water, and water pollution from agricultural and Bosque escarpment, which marks the boundary between human wastes. These alluviated areas provide sand and two major physiographic divisions of gravel for construction. They are normally well drained and Black two major structural-strati- and agriculturally important. graphic craton and East Texas basin. (7) The Brazos and Bosque terraces occur 20 to (2) Waco is underlain by eastward dipping bedrock 125 feet above present river levels. I, II) composed of Cretaceous limestone and Brazos terraces are composed of siliceous gravels and shale beds of the Gulf Coast homocline. This homocline they furnish the principal gravel sources for the IV) is complicated by the north-south trend­ Waco area. Terraces normally support stable, well- ing Balcones fault zone which transects Greater Waco. drained foundation sites for light structures. Brazos Alluvial and terrace deposits of the Bosque and Brazos terraces readily absorb large quantities of waste water, systems overlie Cretaceous bedrock throughout much but because of high permeability, water within the of Greater Waco, especially in east Waco II). terraces is polluted. (3) The geology of Greater Waco, which controls Bosque terraces are composed of limestone gravels or affects foundation properties, excavation problems, with clay cement or binder. These terraces are locally permeability of bedrock, thickness of soil cover, aquifer cemented by calcium carbonate, and they will support potential, blasting hazard, and other important factors, substantial building loads. Bosque terraces are normally exerts a significant control on Waco urban growth thin, absorb moderate quantities of waste water, and and development. produce limited quantities of polluted water during wet (4) Heavy construction in the Waco area will be periods. most affected by bedrock geology of the region. Light (8) Rocks older than Quaternary, which crop out construction conversely will be affected significantly by in the Waco area, include from top to base, Taylor soils developed on bedrock of the Waco area. It is Marl, Austin Chalk, South Bosque Shale, Lake Waco critical that rock and soil behavior be clearly distin­ Formation, Pepper Shale and Del Rio Clay. guished when utilizing and interpreting geological Taylor Marl underlies essentially all of east information. II) (commonly beneath terraces and alluvium). (5) The variety of geologic formations and the local The formation also crops out in the extreme south­ fault pattern create situations where plastic shales and eastern corner of west Waco I). Because of its resistant limestone beds are in contact along narrow plastic nature and high content, Taylor Marl zones or lines. absorbs fluids slowly, and it displays high Foundations designed for structurally competent beds ratios. The marl readily fails under light loads on are inadequate for adjacent plastic bedrock material, gentle slopes. Shallow excavations in the Taylor Forma­ and foundations designed for the plastic bedrock for­ tion are unstable and require shoring. Complex faults mations are over-designed for adjacent resistant bed­ also complicate urban development along the outcrop rock. Excavation methods adopted for plastic clay-rich of this formation. sections are not adequate for more resistant limestone (9) Austin Chalk crops out over the greatest area areas. Slopes which are stable in limestone areas are of west Waco (PI. I). The formation is composed of excessively steep for areas of clay outcrop. Bedding porous chalky limestone beds interstratified with some­ and fractures provide natural partings which expedite what less resistant marl beds. Austin Chalk provides excavation. strong foundations, and it will absorb significant quan­ Permeability of formations is affected by lithology, tities of waste water. Because of the tenacity of chalky faults, and fractures. Faults and joints provide effective limestone beds, relatively steep slopes cut in Austin transmission (in some cases piping) of fluids through Chalk are stable. Shallow excavations do not require rock. internal support. Soils developed on Austin Chalk have Thick soils develop along faults and joints with at­ high shrink-swell ratios. However, Austin soils are tendant problems. Bedding and fractures may serve normally thin, and most structures will, therefore, rest as wave guides, which direct shock (seismic) energy upon unweathered chalk bedrock. In local areas of for distances, creating blasting hazards thick Austin soils, foundation damage is common. related to fault and joint alignments. (10) South Bosque Shale is plastic, calcareous to Major faults influence the depth of aquifers, and noncalcareous, gray shale exposed along the base of may significantly modify water availability, migration the Bosque escarpment beneath Austin Chalk I). and chemistry. South Bosque Shale readily slumps on even gentle Engineering and construction procedures effective in slopes, and failures of foundations, streets, highways, one part of Greater Waco may be wholly inadequate in and septic tanks are common along the South Bosque another part of the city. Shale outcrop. The calcareous lower part of the forma­ (6) Formations which crop out I, II) in the tion is somewhat more stable and permeable than upper Waco area range in age from Recent to Middle Cre­ noncalcareous South Bosque Shale. taceous (table 2). (11) Lake Waco Formation I) is composed of Brazos and Bosque alhtvial deposits are the youngest bentonitic shales interbedded with thin geologic materials in the Waco area. Construction upon limestone beds. The formation is divided into three these units include risks such as occasional flooding, members: An upper Bouldin Member, dominantly lateral migration of river channels, foundation failure fissile shale with some limestone beds from four to six due to plastic nature of substratum, existence of shallow inches thick; a middle Cloice Member, principally 42 BAYLOR GEOLOGICAL STUDIES

calcareous, fissile and a lower Rio Clay absorbs fluids slowly, if at all. Member, dominantly fissile, calcareous shale Rocks older than Del Rio do not crop which includes several limestone beds from one to ten out in the Waco area, but they do crop out west and inches thick. Suitability of Lake Waco outcrops for north of Waco. These Waco subsurface formations construction sites depends largely upon the number and V) include Georgetown Limestone, Edwards thickness of thin interstratified limestone beds. Zones Limestone, Peak Limestone, Walnut Clay, with abundant limestone beds will support substantial Sand, Glen Rose Limestone, Hensel Sand, foundation loads, but plastic clay sections fail under very Pearsall Formation, Limestone, Hosston Sand, small loads and on gentle slopes. Lake Waco clays have and rocks of the pre-Cretaceous Ouachita high ratios, and the formation absorbs Some subsurface formations in the Waco area are fluids very slowly, if at all. significant to urban planning and development because (12) Pepper Shale crops out at the foot of the the}' contain economic materials along outcrops north Bosque escarpment in the extreme southwestern part and west of the Waco area, contain potable water, and of the west Waco area (PI. I). The shale is composed provide permeable reservoirs for subsurface waste of dark, blue-gray, noncalcareous, highly plastic shale. disposal in the Waco area. Pepper Shale is essentially impermeable. Soils which develop on the formation form a highly corrosive en­ Edzvards Limestone provides crushed rock and di­ vironment for buried pipes and metal structures. mension stone within the Waco region. Palu.vy Sand (13) Limestone is dense, discontinuous, re­ contains potable water north and west of Greater Waco. sistant limestone normally less than two feet thick. It is Glen Rose Limestone contains limited of absent throughout much of the Waco area. Buda sulphurous water, and may ultimately provide a dis­ Limestone is, therefore, of little engineering significance. posal reservoir for injected waste fluids. Hensel and The limestone is exposed principally in excavations Hosston sands produce artesian water in the Waco area, north and east of Lake Waco. and they constitute the principal water supply of most (14) Del Rio Clay is gray, plastic, calcareous shale communities in the Heart of Texas. exposed principally in excavations north of Lake Waco. (16) Three summary maps (figs. 4, 5, 6) are pre­ Unweathered clay will support moderate foundation sented, which show suitability of Waco bedrock for loads, but the formation fails plastically when wet. Del foundation, excavation and infiltration.

WELL LOCALITIES Well No. Well Description

1 J. L. Myers No. 1 Tiery. 12 Layne-Texas Company, No. 1 Bryan-Maxwell-Bryan. 2 J. L. Myers & Sons, No. 1 Pardo. 13 Texas Water Company, No. 3 Texas Water Company. 3 J. Myers & Sons, No. 2 McL County is- 14 F. Caraway, 1

No. 1. J. Myers & Sons, 1 J. W. Broughton. 4 Casey & Wimpee, No. 1 Housing Division. 16 Stoner, No. 2 Midway Water Company. 5 City of No. 2 City of Bellmead. 17 C. M. Stoner, No. 1 Midway Water Company. 6 Layne-Texas Company, No. 1 McLennan Comity Water Control Jackson et No. J. D. Lovelace.

District No. 1. 19 Jackson et al., No. 2 J. D. Lovelace. 7 Layne-Texas Company, No. 3 Lacy Lakeview. 20 Midway Park, No. 1 Midway Park.

8 H. C. Buchanan, No. 1 H. C. 21 U. S. Corps of Engineers Core Hole (Station 56.00). 9 Joe No. 1 Paul Shelby. 22 Fulton Place, No. 1 F. M. Orelup. 10 Pure Company, No. 1 water well (Garrison Street). 11 Pure Milk Company, No. 1 water (Jefferson Street). Waco area. to V for electrical and lithologic log of this reference well. GEOLOGY OF WACO 43

ACIDIC EFFLUENT. Sewer wastes which have acidic properties. DIP. The angle and direction of inclination of a sloping bed of ALLUVIATED VALLEY (BOTTOMLANDS). A valley in which sedi­ rock always measured perpendicular to strike. Commonly ments have been deposited by a stream. See Floodplain. expressed in degrees of inclination below horizontal (or ALLUVIUM (Alluvial Deposits, Floodplain Deposits). Sediments in feet per mile) and compass direction of dip. deposited by streams during floods. DIP SLOPE. Sloping topographic surfaces approximately parallel ALTERNATING BEDDING. A sequence of bedded rock composed of to the dip of the underlying inclined rock beds. interlaminated beds of two or more rock types. DISSEMINATED MINERALS. Mineral grains distributed at random AMMONITES. An extinct class of molluscs closely related to the throughout a rock mass. modern Nautilus ; commonly coiled in a plane. DRAG. Minor folding of strata along the walls of a fault AMORPHOUS MATERIAL. Solid material which does not display caused by movement of the beds on either side. significant crystal structure. DRILLER'S LOG. Tabulation of rocks encountered in drilling AQUIFER. A geologic formation which produces water. a well. Recorded by the driller. ARTESIAN WATER. Underground water which rises above the EAGLE FORD PRAIRIE. Prairie region underlain by rocks of the level of the aquifer in wells. Eagle Ford Group. BALCONES FAULT ZONE. Zone of en EAST TEXAS BASIN. Crustal block east of the Balcones fault faults which pass through the Waco area. zone which subsided and was filled with sediments during BANK LOAD DEPOSITS. Fine-grained silts and clays deposited by Mesozoic and Cenozoic time. a river on its floodplain. EDWARDS PLATEAU. A large physiographic region principally BANK STORAGE. Ground water stored in alluvial material along west of San Antonio, composed of high tablelands capped stream banks and derived or charged from the stream. by Edwards Limestone. BED LOAD DEPOSITS. Coarse sand and gravel which move along EH. Oxidation-reduction potential. A scale used (in geology) the floor of the main river channel during flood. to describe the general degree of oxidation of minerals in BEDDING. Stratification in sedimentary rock resulting from rocks deposited in ancient aqueous depositional environments. changes in sediment type or rate of accumulation. ELECTRIC LOG CORRELATION. Determination of equivalence of BEDROCK. Fresh (unweathered) rock material below the lowest geologic units encountered in two or more wells based on soil zones. similarity in recorded electrical log properties. BELTED COASTAL PLAIN. Parallel bands of outcrops bordering ELECTRICAL LOG (E-Log). Record of electrical properties of the coast. rocks encountered in well bore. Printed on scaled paper BENTONITE. group of clay minerals derived from decomposi­ strips. En Echelon FAULTS. Pattern of faults composed of tion of volcanic ash. parallel faults. BIOCHEMICAL PRECIPITATION. Extraction of dissolved solids SHALES. Shales composed of clay materials which water by organisms to build a shell or skeleton. "pop" like popcorn when heated to high temperatures. Used BITUMINOUS MATERIAL. Coal or coal-like material of plant as lightweight aggregate. origin. FACIES. The total aspect of a body of rock which reflects its BLACK OR BLACKLAND PRAIRIE. Originally a fertile grassland origin (composition, sedimentary structures, fossils, etc.). area underlain by Upper Cretaceous shales. Presently al­ FAULT. Fracture along which there has been relative displace­ most wholly in cultivation. ment of the two sides parallel to the fracture. BLOCKY SHALESO R CLAY. Lacking fissility or bedding. Breaks FAULT CONTACT. A contact between two bodies of rock or into irregular masses. formations along a fault. BosQUE ESCARPMENT. The west-facing cuesta which parallels FAULT DISPLACEMENT. Dislocation of a given rock bed or the south bank of the South Bosque River from Moody formation along a fault. Generally measured in feet of to Waco. vertical movement. Commonly fault displacement is re­ CALCAREOUS. Containing or composed of calcium carbonate. ferred to as up-to-the-east, down-to-the-east, down-thrown CALCITE. mineral composed of calcium carbonate (CaCO.s). to the southeast, etc. Principal constituent of limestone. FAULT-LINE SCARP. Escarpment produced by erosion CALCITE VEINS. Tabular masses of calcite cutting across bedding. of beds of resistance brought together by faulting. Common along faults and FAULT SCARP. Escarpment which owes its relief directly to CALCIUM PHOSPHATE. A dark detrital or concretionary bone­ faulting. like material. FAUNA. A natural assemblage of animals. CAPROCK. resistant bed of rock which caps higher hills and FELDSPATHIC. Rock or sediment composed in part of feldspar protects them from rapid erosion. grains. CARBONATE. An informal term referring to minerals composed FILLED BORINGS. Burrows of marine organisms which have been of iron, calcium and magnesium carbonate. For example, filled by sediment and have been preserved in sedimentary calcite. rocks. CEMENTING AGENT. Bonding material in sedimentary rock. Com­ FISSILE. The property of shales which permits them to separate monly calcareous or siliceous. into thin flakes in planes parallel to bedding. CHALK. Porous, fine-grained, soft limestone of marine origin. FLAGSTONE. Rock bed which breaks into thin flat plates of CHERT. (Flint, Jasper). Rock composed of microcrystalline or considerable size. amorphous silica. FLOODPLAIN. The part of the valley floor subject to flooding. CLASTIC DEPOSITS OR DEPOSITION. Accumulation of fragmental FLOODPLAIN DEPOSITS. See Alluvium. sediments such as sand, silt, or clay. FORAMINIFERAL TESTS. The commonly microscopic CLAY. Sediment composed principally of clay minerals less than of a protozoan (one-celled The test is 0.002 mm in diameter. normally composed of calcite or quartz fragments. CLAY MINERALS. A major mineral clan composed of aluminum, silicon and oxygen with lesser amounts of calcium, sodium, FORAMINIFERS. Order of protozoan organisms. potassium and iron. FORMATION. A mappable, traceable body of rock. May be com­ CONGLOMERATE. A rock composed of cemented gravel. posed of a single rock type or a mixture of rocks bounded LIMESTONE. Limestone composed primarily of fossil recognizable beds. shells and shell fragments. FORMATIONAL OR GEOLOGIC CONTACT. or surface be­ CRATON (Texas Craton). Structurally stable crustal block lying tween formations. west of the Balcones fault system. CROSS BEDS. Laminated sediments deposited at sharp angles to FOUNDATION LOAD, SUPPORT STRENGTH, OR ENGINEERING the major bedding planes. Normally indicative of current STRENGTHS. Foundation load refers to the stress per unit action. ... area applied to the earth by a building or structure. Support CUESTA. Asymmetric topographic ridge underlain by gently strength or engineering strength refers to the capacity of dipping resistant bedrock layers. rock materials to support foundation loads. DENDRITIC DRAINAGE PATTERN. Stream system in which the major stream and tributaries form a tree-like pattern. used in this glossary were specifically defined for the DEPOSITIONAL CYCLES. Repetition of sedimentary environments through time, reflected by repetitious alternation of rock Geology of Waco. The glossary is, therefore, oriented toward Central" Texas Geology and Urban Geology. types. 44 BAYLOR GEOLOGICAL STUDIES

FRACTURE. Crack in the rock related to jointing or MASSIVE ANHYDRITE. An informal name given to a subsurface faulting", reflected by alignments visible on outcrops and on member of the Glen Rose Formation composed of lime­ aerial photographs. stone and anhydrite. Anhydrite is a mineral composed of FRIABLE. The tendency for a clastic rock to crumble readily calcium because of the absence of intergrain cement. MEANDER. Large bend in river channel incised into floodplain GEOLOGIC MAP. Map showing geographic distribution of out­ deposits. cropping formations. MEANDER CUTOFFS. Meander loop or bend of a river which GLAUCONITE. soft, green, clay-like mineral composed of was isolated or cut off from the stream when the main hydrated iron aluminum magnesium silicate. channel cut across the loop to shorten its stream course. GLEN ROSE PRAIRIE. Grasslands developed on the outcrop of MEANDER SCARS (Floodplain Scroll). Filled abandoned meander. the Rose Limestone. MECHANICAL WAVE GUIDES. A system of bounding surfaces GRABEN. Down-faulted linear block of earth's crust bounded by which tend to confine and direct earth shock waves in faults. specific directions. CONTACTS. A lithologic transition from one rock MEMBER. A subdivision of a formation. A minor mappable unit type or formation to another. of rock. GRAND PRAIRIE. Grassland developed on Lower Cretaceous METAMORPHOSED. Altered by extreme pressure and/or heat. strata (Washita and Fredericksburg groups). Now cul­ Quartzite of metamorphic origin. tivated areas or grasslands. MICROCRYSTALLINE CALCITE. Limestone composed of microscopic GRAVELS. Unconsolidated sediment composed of pebbles from 2 calcite crystals. to mm in diameter. FORAMINIFERA. type of foraminifer (order of GRAVITY SLUMPING. Failure of rock material or by sliding protozoan) characterized by a distinctly coiled shell or test. and plastic flow down an unsupported face or slope. MONTMORILLONITE. family of minerals which exhibit GROUP. TWO or more superposed formations which are grouped extreme shrink-swell properties. because of related origin and/or composition. NEKTONIC. Refers to swimming marine organisms. GULF COASTAL PLAIN. Extensive physiographic plains extending NERITIC. Marine environment characterized by shallow water from Florida to Yucatan, underlain by Mesozoic and Ceno- (from tide to a depth of 600 feet). zoic rocks. Rounded concretionary bodies which can be separated HEMATITE OR IRON OXIDE. The mineral A common as discrete mineral masses from the formation in which mineral and the principal ore of Has a characteristic they occur. Commonly composed of quartz, calcite, red color when powdered. or hematite. Uniformly dipping rock strata. NONRESISTANT STRATA. Rock beds which readily weather and HYDRATED. Minerals containing water in the crystal structure. erode. Principally shale in the Waco area. HYDROLOGY. The study of the mechanics of water movement. NORMAL FAULT. fault. Fault which results in length­ -. May involve surface or subsurface water. ening of crust. ILLITE. family of clay minerals which display intermediate OFFSET BEDS. Beds or strata which have been fractured and properties. displaced by movement along a fault. INCOMPETENT STRATA. Rocks which yield readily under load Texture of sedimentary rock composed of small ac- or other stresses. cretionary spherical grains, commonly calcite. INFILTRATION. Seepage of water into or through rock. FOLDBELT OR THRUST BELT. Deeply buried, eroded, INFILTRATION OR SEPTIC FIELDS. An area of underground drain­ ancient, folded mountain belt beneath the Balcones fault age of septic sewage effluent. zone. INTERCALATED BEDDING. See Alternating Bedding. OUTCROPO R OUTCROP BELT. Geographic region or belt where JAROSITE. family of complex, yellow, hydrated, a specific rock formation is exposed at the surface or sulfates which form by weathering processes or by covered by mantle. vein origin. OXIDATION. The process of combining with oxygen. For ex­ family of clay minerals which do not exhibit ample, iron will oxidize to various minerals such as hematite shrink-swell properties. An element that has been oxidized has lost LAGOONAL ENVIRONMENT. Sedimentary environment character­ electrons or has become more positive in valence charge. istic of a lagoon or enclosed bay. MATERIAL. Rock material from which a specific soil is LAMPASAS CUT PLAIN. A part of the Grand Prairie (Fred­ derived by weathering and soil-forming processes. ericksburg Group) which has been deeply dissected to PELECYPODS. Clams and related molluscs. An important group produce a rolling plain of Walnut Clay bedrock of bivalved molluscs. scattered bluffs and mesas capped by resistant Edwards PERMEABILITY. The property of a rock which permits it Limestone. transmit fluids. LEACHING. Removal of soluble constituents of rock or soil by PH. Refers to acidity or alkalinity. Scale ranges from extremely natural solutions. acidic (1) to extremely basic (14) ; neutrality is approx­ Sedimentary rock composed of calcite (calcium imately 7. A measure of the hydrogen-ion concentration. carbonate). PHOSPHATIC. Composed largely of calcium phosphate. OR HYDRATED IRON OXIDE. A family of hydrated iron PHYLLITE. Metamorphic rock with characteristics midway be­ oxides which provide the yellow and brown pigments in tween a schist and a slate. many rocks. PHYSIOGRAPHY. In this report, the configuration of land LITHOLOGIC LOG. Description of the rocks encountered in drilling especially the relationship of topography to underlying a well. strata and structure. study of rocks. Informally used to refer to PIG MENTING MATERIAL. Material which provides the color in the composition of rocks. rocks. Normally iron oxide or carbonaceous material. LLANO UPLIFT. The region in which erosion has exposed elevated PINCH OUT. The lateral disappearance of a bed or formation by ancient rocks in the vicinity of Llano, Texas. thinning. Disappearance of a unit commonly called LOAM. A soil composed of a mixture of clay, silt, sand and pinchout. organic matter. POINT BARS. Sand or gravel bars deposited on the inside of a FAULT ZONE. Zone of en down-to-the- river POROSITY. Pore space in a rock or sediment. In this paper it west faults east of the Balcones fault zone. refers to the capacity to store fluids. MANTLE. The layer or "mantle" of loose, incoherent rock PYRITE. Mineral composed of iron sulfide (fool's gold). material which nearly everywhere forms the surface of the QUADRANGLE MAP. Map of a geographic region bounded bv land and rests on bedrock. specific meridians and parallels. MARCASITE. Mineral composed of iron sulfide similar QUARTZ. Silicate mineral which is the dominant con­ to pyrite (fool's gold). stituent of sand and highly resistant to weathering. MARINE REGRESSION. The slow seaward migration of the shore­ QUARTZITE. Rock composed of quartz grains tightly cemented or line. welded by quartz matrix. Extremely resistant to weather­ MARINE ROCKS OR STRATA. Rocks composed of sediments ing ; commonly occurs in terrace gravels. deposited under oceanic conditions. QUARTZOSE. Composed of quartz grains. MARINE TRANSGRESSION. The slow movement of the sea over the REEF AND PATCH REEF FACIES. In this report, parts of the land. Edwards Limestone composed of massive reefs and isolated MARL. Calcareous shale. small reefs with detrital lime.stone in areas. GEOLOGY OF WACO 45

REFRACTION SEISMIC METHODS. Geophysical exploration method sequence, or by distinctive lithology. Similar techniques based upon transmission of elastic waves through earth can be used in tracing subsurface formations. Over great materials. distances, fossils may be used to determine approximate RESISTANT STRATA. Rock beds which weather and erode slowly. time equivalence. Principally limestone in the Waco area. STRATIGRAPHIC POSITION. Position of a bed of rock in a RESTRICTED ENVIRONMENT. Aqueous depositional environment sequence of strata. characterized by limited water circulation. STRATIGRAPHY. The study of the sequence, properties, distribu­ GRANDE EMBAYMENT. A crustal block (or structural basin) tion and origin of stratified rocks. which subsided and filled with sediments principally during STRIKE. Line of intersection between a dipping rock bed and a the Cenozoic Era. Occupies an area of the Gulf Coastal horizontal plane. Normally expressed as a compass di­ Plain along Texas-Mexican border. rection (acute angle from north). ROCK. Aggregate of minerals. CTURAL ALIGNMENTS. Linear features related to fractures IGNEOUS ROCK. ' Rock derived from solidification of visible on aerial photographs, by stream patterns, by soil molten material. color, etc. SEDIMENTARY ROCK. Rock composed of sediments. STRUCTURAL GEOLOGY. That part of geology devoted to the METAMORPHIC ROCK. Rock altered by heat and pressure study of the geometric configuration of rock beds or bodies. from previously existing rocks. MAP. contoured map which illustrates the con­ RUNOFF. The portion of rainfall which enters the drainage sys­ figuration (relative to sea level) of a bed or formation of tems by surface flow. rock. SALINITY. The concentration of dissolved salts in water. SUBSOILS. Lower zones of a soil. Normally measured in parts per million (ppm). GEOLOGY. The study of rocks beneath the surface, A tusk-shaped mollusc. normally based on well information. SCARP. Escarpment or steep face of a cuesta. SUPERPOSITION. Sequence of beds of rock stacked like a deck SCHIST. Metamorphic rock composed of planar and linear min­ of cards. eral grains with parallel orientation. SURFACE GEOLOGY. The study of those rocks exposed at the SEDIMENTARY ENVIRONMENT. The conditions (physical, chem­ surface. ical, and biological) which exist in a specific area receiving SWELLING CLAYS. A family of clay minerals (montmorillonite, sediments. which swell or expand greatly when wet. SEDIMENTARY STRUCTURES. Textural and bedding variations in TAYLOR PRAIRIE. See Black Prairie. clastic sediments resulting from sedimentary processes. TENSIONAL FORCES. Stresses which tend to stretch the rock, Examples are bedding, ripple marks, etc. normally resulting in fractures and faults (normal faults). SELENITE (Gypsum). transparent mineral composed of TERRACE. Elevated remnant of older floodplain deposit left by hydrated calcium downcutting river. SHALE. Bedded rock composed predominantly of clay minerals. THRUST FAULT (Reverse Fault). Compressional fault. Fault SHELF. Shallow submarine platform. displacement in which crust is shortened. process of expansion and contraction which TOP SOIL. The uppermost zone of a soil. occurs in soils, shales or clays containing those clay min­ TOPOGRAPHIC BENCH. Small elevated flat areas along valley erals which expand wet and contract when dry. walls or escarpments, commonly supported by resistant clays have crystal lattices which accept water molecules rock beds. and expand, and conversely, lose water molecules and TRELLIS PATTERN. Parallel stream system (with contract. Forces generated by clays can be short right-angle tributaries) which follows parallel frac­ intense. tures and faults. Mineral composed of iron carbonate UNCONFORMABLE CONTACT OR FORMATIONS. Surface of non- SILICA. silicon dioxide. deposition or erosion separating two formations or beds. SILICEOUS. Pertaining to silica; containing abundant quartz or UNCONFORMITY. See Unconformable Contact. related minerals composed of UNDERREAMED PIERS OR FOOTINGS. Concrete foundation columns SILT. Fine-grained sediment varying in grain size from 0.05 to or beams are larger at the base than at the top. 0.002 mm. VERTEBRATE FOSSILS. Fossilized remains of vertebrate animals. SLATE. Metamorphic rock characterized by well developed Commonly elephant, shark, horse, etc. in vicinity of Waco. cleavage planes. Commonly derived by metamorphism of WATER TABLE. The level of water in a well. Below the water shale. table all pores are filled with water. SLICKENSIDES. Polished and striated (scratched) surface that WEATHERED ROCK. Rock which has been partially decomposed results from abrasion along a fault plane. by the action of water and atmosphere. SOIL. Granular unconsolidated mineral and organic material WEATHERING. The group of processes such as the chemical which develops by soil-forming processes and overlies action of air and rain water, the activities of plants and May or may not have been derived from the under­ bacteria, and the mechanical action of temperature changes lying bedrock. whereby exposed rocks change in character, decay and SOIL MECHANICS. Study of the physical behavior of soil ma­ finally crumble into soil and/or sediment. terial under load or stress. WESTERN CROSS TIMBERS. A belt of sandy SOIL ZONE. Refers to discrete compositional and textural layers soil on the outcrop of Lower Cretaceous sands in Texas. present in some soils. WHITE ROCK ESCARPMENT. Cuesta which is formed by the STRANDLINE. Shoreline. eastward dipping Austin Chalk (locally called the Bosqne STRATIGRAPHIC CORRELATION. Determining equivalence Escarpment). and/or continuity of formations or beds. Continuity can be demonstrated by tracing along the outcrop, by position in a WHITE ROCK PRAIRIE. Prairie region underlain by Austin Chalk. INDEX

Adkins, W. S., 11, 14, 25, 28, 29, Colorado River, 22 ward, O. T., 11, 14, 16, 29 Quaternary 38, 39 Comanche Peak, 38 Hensel Sand, 30, 38, 39 alluvium, 15, 19, 20, 23, 30 Asa. 15 Comanche Peak Limestone, thickness, 30, 39 terraces, 15, 20, 21, 23, 30 Austin, 7, 22, 23, 29 37, 38 water, 18, 39 Ray, J., 34, 35 Austin Chalk, 15, 16, 17, 19, 21, contacts, 38 Hill, R. T., 11, 22, 25, 35, 37, Recent alluvium, 19 22, 23-25, 26, 27, 30 exposures, 38 38, 39 Red River, 22, 25, 37 contacts, 22, 23, 24 thickness, 30, 38 Hog Creek, 21 reef structure, 38 economic geology, 31 water, 30 H. D., 14, 16, 39 resources, 5, 6 excavation difficulty, 25, Comanchean Hood County, 38 Rio Grande exposures, 23, 24 rocks, 18, 35, 37 Hosston Sand, 30, 39 Big Bend of, 35 faults, 16, 24, 25 Series, 30, 34 thickness, 30, 39 embayment, 22 foundations, 17, 24, 31 Conger, R., 14 water, 18, 30, 39 River, 25, 37 infiltration capacity, 25, construction materials Houston. 6 Valley, 35 slope stability, 25, economic geology R. W., 39 Rogers, R. W., 16 soils, 24, 25 Cooper Foundation, 14 Indian villages, San Antonio, 6, 23 support strength, 24, 31 Corpus Christi. 6 Indians, San Fernando 7 thickness, 24, 30 Cottonwood Creek, 15, 20 Intercounty Regional Planning San Marcos, 7 water, 25, 30 Cow Creek Limestone, Commission, Denver, 6 sand, 20, 30, 31, 38, 39 weathering, 24 see Pearsall Formation Johnson, C, 34 Satin field, 35 "Austin limestone," 23 Crawford, 38 Jurassic, Seewald, O., 24 Austin, S. F., 14 Cretaceous rocks, 15, 16, 22, 30, 38 evaporite deposits, 18 Seitz. F., 5 Balcones fault Dallas. 6, 16, 24 rocks, 39 23 system, 16, 18, 22, 29 Rio, 35 Shale, ' Shoal Creek Limestone," 34 zone, 16, 17. 29 Del Rio Clay, 20, 22, 30, 34, see Georgetown Formation Shumard, B. F., 23 Baldwin, D., 14 35, 37 Lake Waco, 14, 15, 21, 28, 29, 35 Silver, B. A., 28, 29 Barnard, G., 14 contacts, 29, 34, 35, 37 dam, 20, 28 (old). 37, 38 Limestone, 30, 38, 39 Barton Creek, 38 drainage pattern, 35 Lake Waco Formation, 22, 25. 26, thickness, 30, 39 A. O., 16, 22 economic geology, 31 28, 29, 30 Soil Conservation Service, Beaver, H. H., 18 excavation difficulties, 31, 37 contacts, 26, 28, 29 soils, corrosive, Bellmead, 14 exposures, 35 drainage pattern, 29 Somervell County, 38 Bell's Hill, 15, 16 foundations, 31 economic geology, 31 South Community, 27 Belton, 29 infiltration capacity, 37 excavation difficulties, 29, South Bosque oil field, 38 Beverly Hills, 15 slope stability, 31, 37 exposures, 28 South Bosque River, 14, 15, 17, Black Prairie, 14, 15, 23 soils, 37 foundations, 29, 29. 37 "Blue Bluffs division," 22 support strength, 31, 37 infiltration capacity, 29, 31 South Bosque Shale, 22, 24, 25-28. Member, 28 thickness, 30, slope stabihty, 29, 31 30, 34 contacts, 28 weathering, 35 soils, 29 contacts. 22, 26 see South Bosque Limestone, support strength, 29, 31 economic geology, 27, 31 thickness, 28 see Georgetown Formation thickness, 28, 30 excavation difficulty, 28, Bosque County. 38 Denver, 6 water, 29, 30 exposures, 25. 26 Deussen, A., 11 weathering. 29 foundations, 31 Bosque escarpment, 15, 16, 17, 18, Lampasas Cut Plain, 37, 38 23. 24, 25, 27. 28. 29, 34. 37 dip, 7 infiltration capacity, 27, Bosque River, 15, 16, 20. 37 Dixon, J. W., 14, 37 Limestone 22 31, 34 Llano, 29 slope stability, 25, 27, 31 alluvium, 15, 16, 19, 20 21, Duck Creek Limestone, 37 see Georgetown Formation uplift, 16 soils, 26 23, 30 Lonsdale. J. T., 29 support strength. 27, economic geology, 20, 31 Eagle Ford, 25 Eagle Ford Group, 15, 22, 25, 28, Los Angeles, 7 thickness, 25, 30 exposures, 20 Lover's Leap, 24 water, flood hazard, 20 30. 34 see South Bosque Lake Lower Taylor Marl, 22, 24 weathering, 26 foundations, 20 contacts, 22, 23 Steinbeck Bend, 15, 22 ground water, 20 Waco Formation Eagle Pass, 34 drainage pattern, 22 Stephenson. L. W., 22, 23, 24, 25, capacity, 20 exposures. 22 29, 34, 35. 37 soils, 20 East Texas basin, 16, 18, 22, 25, 28. 34, 39 faults. 22 storm drainage, Waco, 15 terraces, 16, 20, 21, 23, 30, foundations. 23 strike, 17 34, 35 Eastland Lake, 15 Edwards Limestone, 15, 21, 30, infiltration capacity, 23 Taylor. 22 economic geology, see Taylor Marl Taylor Marl, 15, 16, 17, 19, 22, 30 exposures, 37, 38 contacts. 37, 38 support strength, 22 contacts, 22, 24 foundations, 21 thickness, 22 economic geology. 31 ground water, 21 economic geology, 31, 38 exposures, 38 weathering, 22 excavation difficulties, 23, 31 infiltration capacity, Lozo. F. E., 25, 29. 38 exposures, 22 soils, 21 thickness, 38 water, 30, 38 Main Street Limestone, 20, faults, 16, 17, 23 valley, 16, 19, 20 see Georgetown Formation foundations, 23, 21 Edwards Plateau, 38 elevations, 16 Marathon, infiltration capacity, 23, 31 Bouldin Member, 28 Mart, 18 slope stability, 23, contacts, 28 Mott, 21 Erath, G. B., 14 McAtee, J., 34 soils, 23 see Lake Waco Formation evaporite deposits, 18 R. L., 14 support 23, thickness. 28 expanded aggregate, 27, McLennan, thickness, 22, 30 Brazos River, 14, 15, 16, 20, 22. fault contact, 22 meander scars, 19 water, 23, 30 23, 28 faults, 16, 17 megapoli, 6 weathering, 23 alluvium. 14, 20, 21 delineation, 17, 18 Mexia fault zone, 16 Tehuacana Creek, 15, 22 23, 30 drainage control, 22, 29 Middle Bosque River, 21, 38 Temple, 7 economic geology, 20, 31 fluid conduction, Moody, 25, terraces, 15, 20, 21, 23 exposures, mechanical guides, 18, municipal engineering. 7 Tertiary rocks, 16 flood hazard, 19 quarrying aid. 18 municipal resources, 6 Texas craton, foundations, 19 water wells near, municipal water. 6 Texas Highway Department, 14 ground water, 19 weathering rates along, 17 Group, 22 Texas Water Development Board, 14 infiltration capacity, 20 P. T.. 37, 39 New 7 topsoil, 20 soils, 19 floodplain scrolls, New York. 7 Trading House Creek, 14, 22 terraces, 15, 17, 20, 21, 22, Fort Fisher, North Bosque River, 21, 37 Trinity aquifer, 30, 38, 39 23, 30 Fort Worth, 6 Oglesby, 38 Trinity Group, 30. economic geology, 21, 31 Fort Worth 37 Ouachita 16, 18, 19, United States Geological Survey, 11 exposures, 21 see Georgetown 38. 39 Universal Atlas Cement ground water, 21 Frederirksburg Group, 30, 37, 38 Pace. L., 11. 22 27 infiltration capacity, 21 Frio County, 39 Paleozoic rocks. 37. 39 Upper Taylor Marl, 22 soils. 21 Frost. G.. 38 Sand, 30, 37. 38 see Taylor Marl tributary drainage pattern, 15 Gatesville, 38 contacts, 38 Uvalde, 29 valley, 15, 16, 19, 23 Georgetown. 37 economic geology. 31, 38 (oil) Valley Mills. 38 Bronaugh, R. 19, 20 Georgetown Limestone, 20, exposures, 38 Vaughan, T. W., 34, 35, 37 Brown, L. F., Jr., 14 35, 37 thickness. 30. 38 Hospital area, Buda, 34 contacts, 35, 37 water. 30. 38 volcanic ash, 28 Buda Limestone, 22, 30, 34, 35 economic geology. Paluxy 38 Waco Aggregate Company, 27 contacts, 29, 34 excavation difficulties, Pawpaw Shale, 37 Waco Creek, 15, 20, 22 economic geology (oil). 35 exposures. 37 see Georgetown Formation Walnut Clay. 30, 37, 38 excavation difficulty, infiltration rate. Pearsall Formation, 38, 39 contacts, 38 exposures. 34 slope stability, 31, 37 thickness, 39 economic geology. 31 foundations, 31, 35 support strength, water, 39 exposures, 38 infiltration capacity, 35 thickness. 30 Pecan Gap Chalk. 22 thickness. 30. 38 slope stability, 31 water, 30 see Taylor Marl water. 30 soils, 35 Glen Rose Prairie, 38 Pendleton, 35 Walnut Springs, support strength. 31, 35 Glen Rose Limestone, 16, 30. Pepper Creek, 29 Washita Group, 15. 30. 34 thickness. 30, 34 38, 39 Pepper Shale, 22, 29, 30, 34 Washita Prairie, 15, 34, 35, 37 water, 30 contacts, 38 contacts, 29, 34, 35 water, 6. 30 Burnet County, 39 economic geology, 31 excavation difficulties, 34 weathering rates, Cameron Park, 16, 24 exposures, 38 exposures, 29 Weeks, A. W., 16 cement, 27 foundations, 34 Weno Limestone, ceramic clays, 20, thickness. 30, 38 infiltration capacity, 34 see Georgetown Formation Chambers, T. J., 14 water, 18, 30, 39 slope stability, 34 Western Cross Timbers, 39 Chamness, R., 26, 28 Glen Rose Prairie, 38 soils, 34 White Rock Creek, 16, 22, 23 7 Goodson, J. L., support strength, 31, 34 White Rock escarpment, China Springs. 34, 35, 38 Grand Prairie, 14, thickness, 29. 30 White Rock Prairie, 24 city geologic map, 7 gravel. 20, 21, 23, 31 water, 34 Williams Creek. 22 city geologist, 7 Gulf Coastal Plain, 15, 16 weathering, 29 Williamson County, climate, 14 Pleistocene terraces, 20, 30 Wilmarth. M. G., 23, 34 Cloice Branch, 25 rocks, 16. 22, 23, 25, 29 pointbar deposits, 19 Wolfe City Sand. 22 Cloice Member, 28 Series, 30 population growth, 5 see Taylor Marl contacts, 28 Hammett Shale. Prather, J. K., 25 Woodbine Sand, 29, 34 see Lake Waco Formation see Pearsall Formation quarrying, Woodway, 28 Harris Creek, 21 BAYLOR GEOLOGICAL

Baylor Geological Society 117. Shale environments of the mid-Cretaceous Central field guide. A. O., Johnson, 101. Type electric log of County. 1"-100'; C. F., and Silver, B. A,, 1964. $2.00 per copy. $2.00. 118. Geology and the City of guide to urban prob­ 102. Reptile of flying and swimming rep­ lems, 1964. $2.00 per copy. tiles. $0.10 each. Comparison of the dinosaurs. $0.10 each. 103. Guide to the mid-Cretaceous geology of central Texas, Baylor Geological Studies May, 19S8. per copy. 104. Location map of logged wells in McLennan County, 1959. 1. Holloway, Harold D. (1961) The Lower Cretaceous l"-lmile, $7.50 per copy. Trinity aquifers, McLennan County, Texas: Baylor Geo­ 105. Layman's guide to the geology of central Texas, 1959. logical Studies Bull. No, 1 (Fall). $1.00 per copy. Out Out of print. of print. 106. Collector's guide to the geology of central Texas, 1959. 2. William A. (1962) The Lower Cretaceous Paluxy Out of print. Sand in central Baylor Geological Studies Bull. 107. One hundred million years in McLennan County, 1960. No. 4 (Spring). $1.00 per copy. Out of print. 3. Henningsen, E. Robert (1962) Water diagenesis in Lower Cretaceous Trinity aquifers of central Baylor 108. Cretaceous stratigraphy of the Grand and Black Prairies, Geological Studies Bull. No. 3 (Fall). $1.00 per copy. 1960. $3.50 per copy, 4. Silver, Burr A. (1963) The Bluebonnet Member, Lake 109. Popular geology of central Texas, west central McLennan Waco Formation (Upper Cretaceous), central County, 1960. Out of print. lagoonal deposit: Baylor Geological Studies Bull, No. 4 110. Popular geology of central Texas, County, 1961. (Spring). $1.00 per copy. $1.00 per copy. Out of print. Brown, Johnnie B. (1963) The role of geology in a Popular geology of central Texas, northwestern McLennan unified conservation Flat Top Ranch, Bosque County, 1961. $1.00 per copy. Out of print. County, Texas: Baylor Geological Studies Bull. No. 5 112. Popular geology of central Texas, southwestern McLennan (Fall). $1.00 per copy. County and eastern Coryell County, 1962. $1.00 per copy. 6. Beall, Arthur O., Jr. (1964) Stratigraphy of the Taylor Out of print. Formation (Upper Cretaceous), east-central 113. Upper Cretaceous and Lower Tertiary rocks in east central Baylor Geological Studies Bull. No. 6 (Spring). $1.00 Texas, Fred B. Smith, Leader, 1962. $1.00 per copy. per copy. 114. Precambrian igneous rocks of the Wichita Mountains, 7. Spencer, Jean M. (1964) Geologic factors controlling Oklahoma, Walter T. Huang, Leader, 1962, $1.00 per mutation and Baylor Geological copy. Out of print. Studies Bull. No. 7 (Fall). $1.00 per copy. 115. Why teach geology? A discussion of the importance and 8. Urban geology of Greater I: Geology cost of teaching geology in high schools, junior colleges Geology and urban development by P. T, Geology and smaller 4-year institutions. Free upon request. 27pp. of Waco by J. M. Baylor Geological Studies Bull. (1961). No. 8 (Spring). A series on urban geology in cooperation Popular geology of central Texas: The hill with Cooper Foundation of Waco. $1.00. McLennan, Coryell and Bosque counties, 1963. $1.00 per available from Baylor Geological Society or copy. Baylor Geological Studies, Baylor University, Waco, Texas. C

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