DESCRIPTION OF THE PIKES PEAK SHEET.

GEOGRAPHIC RELATIONS. sparingly present. Various species of cactus and its dikes cut the coarser variety, an admixture of "gneissoid granite "is applicable to the rock of other plants of dry climates are found in the hornblende causes a darker tone. considerable areas. The Pikes peak atlas sheet embraces the terri­ lower portions of the area. This fine grained granite cuts the coarser Gneisses of doubtful origin. Occurring with tory between the meridians of 105° and 105° 30' grained in many dikes, and also forms large areas certain of the supposed Algonkian quartzites, or west longitude, and the parallels of 38° 30' and DESCRIPTION OF ROCK FORMATIONS. of uniform rock in the plateau region west of as separate inclusions in granite, are gneisses 39° north latitude. This area is 34'5 miles long, As a preliminary to a general sketch of the Pikes peak. Apparently the greater part of this which are not demonstrably derived from granite. north and south, and 27 miles wide, and hence geology of the Pikes peak district it is necessary type belongs to one period of eruption, but it is These are usually fine banded rocks, which are contains 931*5 square miles. It includes portions concisely to describe the various rock formations by no means certain that all the dikes of fine rich in mica, or show a marked alternation of dark of Fremont, El Paso and Park counties. entering prominently into its constitution and grained granite found in the coarser rock belong and light colored minerals. Some of them have TOPOGRAPHIC FEATURES. recognized upon the map. They belong to the to one period. a development of fibrolite and almost grade into three great classes of igneous, sedimentary and Minor granite types. On the western and some of the Algonkian quartzites impregnated Hellef. The area is almost wholly mountainous. metamorphic rocks, but will not be treated in southern slopes of Pikes peak, generally above with secondary minerals. It is quite probable, On the eastern side is the crest of the Colorado strictly corresponding groups because the gneisses, 11,500 feet, there are several masses of a porphy­ indeed, that the fragments in granite represent range, including its culminating point, Pikes peak, the leading metamorphic rocks, are so intimately ritic granite whose constituents are the same as in products of metamorphism of Algonkian strata, and including also a part of the rather abrupt connected with the granites that these two can the main type, but both red feldspar and quartz and also the true Archean gneisses upon which southern end of this range as it dies out en echelon. best be described together. The later igneous are developed in crystals lying in a distinctly the Algonkian beds were deposited. The central and western portions of the district rocks are so far removed from the granites in granular mass of the same minerals. The feld­ Schists. Rocks possessing so perfect a degree form essentially a high plateau, penetrated on the time and conditions of origin that they may well spars are never so large as in the Pikes peak type, of foliation that they may be properly termed south by the narrow valley which will hereafter be considered by themselves. and transitions are rare. This variety seems to schists are of very subordinate development in be referred to as Garden park bay. The most GRANITE AND METAMORPHIC ROCKS. represent a granite cutting the main type. this district. In some places on and near certain prominent topographic feature of the region is the Certain areas contain a fine grained granite planes the gneissic structure gives way to a fine GRANITE. mass of Pikes peak, which rises to an elevation of which is almost white and its feldspars are more schistosity, muscovite replacing feldspar, and a 14,083 feet above sea level. On the east the de­ G-eneral statement. The southern portion of largely plagioclase than in the main fine grained mica-schist results. But the most pronounced scent of 8,000 feet to the plains takes place with­ the Colorado range is mainly made up of granite type. This seems to be a distinct type but it was schists are found as inclusions in granite, notably in eight miles, but is broken by many smaller and of the gneissoid rocks derived from it. There not found in connection with the more common in the Cripple Creek district. These seem to mountain and foot-hill masses lying in the area of are several types which are plainly products of fine grained granite to which it is related. represent earthy Algonkian quartzites metamor­ the Colorado Springs sheet. West of the peak different intrusions, and many varieties whose Another variety of undetermined importance phosed by a great development of mica, or of the descent is rather abrupt to a general plateau significance can be determined only after long occurs in the hills north of the Platte river. It is fibrolite. between 8,500 and 10,000 feet altitude, which study of a large field. The facies, or local varia­ characterized by a development of the pinkish Chloritic or amphibolic schists locally result stretches westward for many miles, and is practic­ tions within a given rock body, often differ more feldspar in small crystals not much larger than from the squeezing of dikes or small masses of ally the level of the great South park. among themselves than masses of independent the irregular grains of quartz and feldspar about ancient basic igneous rocks, as may be seen near The relation of the Pikes peak elevation to this origin. The chemical composition of most of the them. This rock has quartz and biotite in about Rocky, and in the southwestern corner of the dis­ plateau is brought out by the profile section B-B, different granites is nearly the same, and the the same development as the common fine grained trict. extending from Pikes peak to the Platte river marked differences arise chiefly from differences granite but its eruption appears to have occurred SEDIMENTARY FORMATIONS. canyon, shown on the structure section sheet of of color or else from variation in structure due to after the movements -which produced gneissoid the folio. conditions of consolidation. structure in all other types of the district, and ALGONKIAN PEEIOD. To the south the plateau is deeply scored by Within the area of the Pike's peak sheet granite hence to be distinct. The distinctly stratified quartzites and allied many canyons of comparatively recent erosion, appears in many more or less marked varieties, Coarse granitic dikes and veins. All the granites rocks found as inclusions in granite and gneiss which cut nearly to the level of the plains, at but as these are not differentiated on the map, and are traversed by dikes of very coarse grained are obviously the oldest sedimentary rocks of the about 6,000 feet. The greatest elevation is that as, indeed, the relationships of most of them were granite usually designated as pegmatite, in which district. They are at present known only in de­ of Pikes peak, and the least that of Oil creek, as not worked out, a characterization of only the microcline, orthoclase, albite, oligoclase, quartz, tached masses and are therefore not given a for­ it crosses the southern boundary of the area at most important types must suffice. There are two biotite, muscovite and occasionally other minerals mation name. The largest and most homogeneous about 5,500 feet above sea level. types which are especially prominent as occurring are developed in large individuals and are often of these masses is that shown in Wilson park. Drainage. The drainage of the district is by in very large bodies, and contrasting distinctly in segregated somewhat in different parts of the dike. Here there is exposed a section nearly 4,000 feet tributaries of the South Platte and Arkansas structure: These pegmatite dikes are abundant only in the in thickness of white or bluish gray quartzites, rivers. In the northwestern corner the South The Pikes peak granite. The mass of Pikes region near the Platte river. standing on edge and exposed on the strike for Platte river issues from South park on the line of peak is principally made up of a single granite The fine crystals of Amazonstone, smoky quartz, about 5 miles. They are cut off on the southwest the map and cuts its way through the Eleven type, belonging to what is apparently one great topaz, phenacite, and other rare minerals which by granite, and at the northeast pass under the Mile canyon, _ curving in its course from, east to body extending for many miles in all directions. have made the Pikes peak region famous, have sedimentary rocks of Garden park. Granite dikes north. Almost the entire northern third of the In the summit pyramid, above 13,000 feet, there been found most abundantly some miles south­ penetrate them at various places. A narrower district is drained into the Platte, either directly, are several intersecting types. The main granite east of the summit of the peak within the area of belt of quartzite appears in Cooper mountain, east by Twin creek, or through branches of Trout type is a very coarse grained biotite-granite, or the Colorado Springs sheet. But some of the of Garden park, trending northwest. creek which passes north through Manitou park. granitite, in most places of pronounced red color largest and finest specimens of these four minerals Another important mass is that forming a ridge In the northeastern corner of the map area is due to a pigment of hydrous iron oxide which have been obtained from Crystal peak, north west of Florissant, a portion of which is known as the head of Fountain creek, which courses south conspicuously impregnates the feldspars. Its of Florissant. These minerals occur in vein-like Blue mountain. The ridge consists of fibrolitic of east to its debouchure upon the plains at main constituents are the potash feldspars, micro- masses similar to the pegmatite dikes, except that quartzite with a small and variable amount of Manitou Springs, and thence finds its way south­ line and orthoclase, often intergrown after the a free space of variable relationship to the vein feldspar. This mass is also cut by granite dikes ward to the Arkansas. The remaining two-thirds manner of perthite, with plagioclase, quartz and material has allowed development of crystal faces. and is entirely surrounded by granite. of the area is drained by direct tributaries of the biotite. Zircon, apatite, allanite, rutile and other The presence of fluorite, cryolite, topaz, etc., On the northern border of the district, near Arkansas, the most important of which are Oil rare accessory minerals are present with more or testifies to the presence of fluorine in large amount Rocky, is an area of quartzites and schistose rocks creek, Beaver creek and Currant creek. These less constancy. during the formation of these vein minerals. some of which contain pyroxene and garnet. are the streams which have cut the numerous deep Feldspar is the strongly predominant element Cryolite is not found within the area of this These rocks are cut by granite but the area canyons in the granite plateau. The Royal Gorge of the rock and the variations in its development sheet. It appears as a local filling of residual widens to the northwest, beyond the region visited, of the Arkansas approaches at its upper end to cause the principal structural modifications. Some­ spaces in certain veins, after the formation of the and it may expand in that direction to represent within one mile of the southern map line, south of times the grains of quartz and feldspar are of other minerals. [See 6 in the list at the end.] the formation in situ where it is not entirely en­ West Eight Mile park. nearly the same size but ordinarily the feldspar closed by granite. Thousands of much smaller Culture. In spite of its proximity to the earli­ grains are the larger. By a formation of distinct METAMOEPHIC EOCKS. fragments of quartzite and fibrolitic or micaceous est settled portion of Colorado the district of the crystals, often very sharply defined and sometimes Relation of gneiss to granite. Nearly all of schists are included in granite and gneiss of the Pikes peak sheet had no important settlement un­ as much as three inches long, though usually less the rocks of the Pikes peak district which may district. til the mines of Cripple Creek were discovered. than half that size, there arises a porphyritic be called gneisses are practically mineralogical The base of the known Paleozoic section in Along the line now followed by the Colorado structure and the rock becomes a granite-porphyry. equivalents of the granites above described but Colorado is an upper Cambrian quartzite which Midland railroad ran the old stage line from This type is well developed at Raspberry moun­ possess a more or less marked foliated structure. in the Colorado range rests upon the granite and Colorado Springs through South park to Lead- tain, and in other places. Biotite occurs in single Muscovite is the only mineral of much importance gneiss containing these quartzite inclusions. In ville, and Florissant has long been a small village. leaves, large or small, or in clusters of small flakes not characteristic of the granites. The massive the light of present knowledge concerning pre- The plateau region is arid but affords extensive which have the effect of large ones. granite is so frequently found grading insensibly Cambrian sediments in the West it is deemed grazing lands for cattle. In Garden park and at In the Pike's peak type proper, biotite is quite but rapidly into foliated gneiss that there can be better to refer the included sedimentary rocks to certain places in the upper valley of Oil creek, subordinate, but in the region on either side of no question of the derivation of most of the the Algonkian rather than to assume that the and in Currant creek, there are bottom lands the Platte river, and in several places in the south­ gneisses from the granites under the influence of a period of their deposition, as well as that of the which through irrigation yield good crops of hay, western portion of the districts, a large increase in great pressure. granite eruptions, and still further that of meta­ and on Beaver creek in the area of the sediment­ amount of black mica greatly changes the appear­ The plainest instance of the transformation of morphism, producing the gneisses, are all within ary rocks is a small district where fruit is easily ance of the rock. granite into gneiss is exhibited by the coarse por­ the lower and middle Cambrian. grown. The fine grained granite. In marked contrast phyritic granite, whose large feldspar crystals, The northern and western slopes of Pikes peak to the Pikes peak type is a characteristically fine with sharp angles, become gradually distorted, CAMBEIAN PEEIOD. were at one time thickly covered with a luxuriant and even grained reddish or pinkish granite which crushed and drawn out into " eyes " or flat lenses, No Cambrian formation is represented upon the forest of spruce which many years ago was large­ is poor in mica; while its particles are large with mica leaves wrapped about them. This map, although it is probable that a small thickness ly burned over and is now replaced by a dense enough to be easily distinguished by the naked change can sometimes be seen within two or of quartzite and of cherty limestone below the Mani­ growth of aspen. Over the general plateau coun­ eye, it derives its general aspect from the abund­ three feet. In the even grained granites the tou Silurian limestone belong to that period. In try there is a struggling growth of spruce and of ant f eldspathic element. This rock varies little in foliation is marked by the parallel position of the Manitou park and near Manitou Springs brachio- pifion pine, and in the lower ground of Garden structure and seldom in mineral constitution. It mica leaves, muscovite being commonly associ­ pod shells, Lingulepis and Obolella, have been park and along the base of the mountains pifion is sometimes deep red and in other places pale ated with biotite. The intermediate structural found in quartzites beneath the Manitou limestone, pine, cedar and scrub oak are quite uniformly but pink. In the summit cone of Pikes Peak, where stages are so abundant that the expression and the cherty limestone at the base of the series in Garden park has yielded a trilobite, Ptychoparia. been found in any other part of the West. Its JURATRIAS PERIOD. have been much greater than that of the beds still These forms indicate upper Cambrian deposits, present limitation eastward from Garden park, on The Morrison formation. The earliest Mesozoic preserved. but the extreme thinness of the beds in question the slopes of the range, is by erosion which took sediments are prevailingly greenish, pinkish or The deposits in the Florissant lake were almost and their variable local development makes their place after the deposition of the Millsap limestone. gray shales and marls. Sandstone occurs at the wholly of volcanic ashes which were probably representation on the map impracticable and they The name Fremont is that of the county con­ base and is also intercalated at numerous horizons showered upon its waters, forming soft and are therefore included with the Manitou limestone. taining all of the known exposures of this lime­ in the upper part of the section with varying de­ crumbling tuffs and mud shales. The total thick­ stone. ness of strata now preserved is only about 50 feet, SILURIAN PERIOD. velopment. The total thickness of the Morrison CARBONIFEROUS PERIOD. formation in Garden park is about 350 feet. In mainly in thin layers of very fine grain, alternat­ The Silurian section of the upturned zone be­ The Millsap limestone. This formation is found a sandstone horizon about 100 feet from the top ing every few inches with coarser ones, while tween Canyon City and Garden park has been only in local remnants resting upon the Fremont of the series has been found a large vertebrate heavier banks several feet in thickness occur in studied in detail by Mr. C. D. Walcott, and limestone in Garden park and along the western fauna belonging in this locality especially to the some places. divided into three important formations, distin­ line toward Canyon city. It is specially well ex­ Dinosauria, many forms of which have been de­ The predominant material is andesitic in char­ guishable by their rich invertebrate faunas and posed in the angle between Oil and Millsap creeks scribed by O. C. Marsh. Fresh water shells asso­ acter, with detritus of basalt and rhyolite, and prob­ also by stratigraphic data, to which he has given and is named from this locality. The formation ciated with these remains indicate the character ably belongs to the earliest eruptions of the vol­ the names here used. [8.] is now represented by about 30 feet of thinly of the sea in which the rocks were deposited. canic center which lies westward of the map area. The Manitou limestone. This is the lowest bedded, variegated, dolomitic limestone, with a Gypsum is locally developed and becomes promi­ Dark basaltic breccia, and remnants of rhyolitic Silurian formation. In Garden park it consists of few thin sandstone layers. Chert nodules in the nent to the east. A thin limestone often forms flows rest upon the Florissant tuff at many points. fine grained, pink or reddish dolomite, less than upper limestone layers carry casts of Spirifera the base of the formation. The name is given The conditions under which the Florissant tuff 100 feet thick, and contains Ophileta, Camarella, rockymontana and Athyris subtilita, characteristic from the classic locality at Morrison, near Denver, was deposited were highly favorable to the burial and a few other invertebrate fossils characteristic forms of the Carboniferous throughout the West. where the first gigantic Dinosaurs from this for­ and preservation of the subtropical fauna and flora of the lower Silurian formation in the section at The long period between the Fremont and Mill- mation were obtained. of the period. The insect fauna preserved is es­ Manitou Springs and in Manitou park, whence the sap epochs seems to have been one of elevation The Morrison strata rest with apparent con­ pecially wonderful. Many thousand specimens name is derived. This limestone is best seen in and erosion, for while there is seeming conformity formity upon the Fountain grits in the main have been collected, since the discovery of the beds the upper part of Garden park. On the slopes of between the two limestones in local exposures, the foot-hill section, but in Twelve Mile park and in and although the material has been but partially the Colorado range to the east the formation has Millsap strata of Garden park rest upon much the higher plateau region to the north they lie described it is sufficiently known to prove that no been much eroded, and it is wanting in many lower beds of the Fremont than at exposures directly upon granite. There is thus a great other locality in America, and but one or two in places east of Eight Mile canyon. nearer Canyon city, where an upper division of the stratigraphic break between the Morrison and the Europe can compare with Florissant in variety of The limestone below the Fountain beds in the Fremont is preserved. In lithological character Fountain formations the extent of which is at insect forms preserved. northeastern corner of the area is connected di­ the Millsap limestone is peculiar, and the few present unknown. A similar series of beds be­ In addition to the insects there are a few birds, rectly with the typical locality at the north end of fossils thus far obtained from it have such a wide neath the Dakota formation of the Cretaceous fishes and mollusks, and a very large fossil flora. Manitou park, but the steeply upturned beds are range that close correlation of these strata with period, occurring on the Pacific slope in Colorado, The fossil remains agree in indicating that the much thinner than to the north, partly through those of other sections is as yet impossible. has been named the Gunnison formation by Mr. climate of the period was warm, and the age of shearing, partly by erosion preceding the Foun­ The Fountain formation. Under this name are G. H. Eldridge, in the description of the Crested the formation is shown by them to be late Eocene tain period. The formation is not doloniitic in included a series of red sandstones, grits and con­ Butte sheet. (Oligocene). [5, 7.] this vicinity. glomerates, a part of the so-called "Red beds," The High park lake beds. To the west of Oil CRETACEOUS PERIOD. The Harding sandstone. This very character­ found in typical development on Fountain creek creek, on the granite plateau, lies High park, a istic formation is made up predominantly of fine below Manitou Springs, and at the head of the The Dakota formation. The Morrison forma­ small depression containing remnants of a series and even grained, saccharoidal sandstone in alter­ same stream in the northeastern corner of the tion is followed with apparent conformity by of local sandstones and conglomerates lying either nating banks of light gray and pinkish or vari­ Pikes peak area hence the local name here ap­ about 300 feet of fine white or gray sandstone, upon granite or upon a thin rhyolite flow. The egated colors, with a few bands of dark red or plied. The formation in Garden park seems called the Dakota sandstone, usually friable and conglomerate is characterized by pebbles of the purplish sandy shale. The maximum thickness is practically identical lithologically with that of the of uniform texture. At or near the base there is extremely hard Algonkian quartzite together with about 100 feet. The lower part is sometimes former area, and the same name is applied to the usually a fine conglomerate, the pebbles of which some of granite and gneiss. No fossils are known calcareous and locally develops into a thin, fine beds of both regions. are variously colored chert or white quartz. from these strata and they appear to be older than grained dolomite. The beds of the upper exposures on Fountain Midway in the series are several layers of dark the adjacent volcanic breccia, as they contain no This horizon is characterized by numerous creek belong to the basin of Manitou park. They shale, locally developed into pure fire clay of debris of such material. In the hills east of High plates and scales of ganoid fishes and by a chord al are chiefly coarse grained, crumbling, arkose sand­ economic importance. Where steeply upturned park the conglomerate is seen between rhyolite sheath of a selachian form. It carries also a rich stones, in heavy banks showing cross-bedding. the Dakota characteristically forms the capping and phonolite flows. A very small remnant of invertebrate fauna indicating close correlation They are locally conglomeritic, mottled with gray of hogback ridges, or of gentle mesa-like slopes, as the High Park conglomerates is present on the with the lower Trenton of New York. The fishes and various light shades of red, through irregular to the south of Garden park. This formation is rhyolite sheet capping Red ridge, 500 feet above of the Harding formation are the oldest known, distribution of the coloring matter. Near the found above the Morrison in Twelve Mile park, the present level of High park. and belong to types not elsewhere found below base and at intervals throughout the series are and in small remnants upon the granite to the The Alnwick lake beds. In the valley of Oil the Devonian. very dark red or purplish layers of arenaceous north. Many fossil leaves are found in the thin creek about Alnwick is a local lake basin confined The Harding sandstone is not found in Manitou shale or fine grained sandstone. The thickness of shale layers at various horizons in the formation. to the present valley of Oil creek, and its western park, or at Manitou Springs, and has not been the formation near Woodland park is estimated The Colorado formation. The Dakota is suc­ tributary West Four Mile creek. The deposits in identified at any other locality, but similar fish at nearly 1,000 feet. ceeded by a series of dark or gray shales with a this lake were fine grained sandstone and con­ remains have been discovered by Mr. G. H. Eld- The characteristics above noted are also found complex of fine limestone beds about midway in glomerate, among the pebbles of the latter being ridge in Gunnison county, Colorado, in lower in the lower 1,000 feet of the section of reddish the series, and with a brownish sandstone near the representatives of the volcanic series to the west. Silurian strata not yet differentiated in a manner sandstones and grits to the east of Manitou Springs, top. The thickness displayed on West Wilson This lake was therefore apparently younger than corresponding to the Garden park section. In referred by Hayden to the upper Carboniferous, creek near the southern border of the map is about that of High park. No fossil remains have been Garden park the Harding sandstone rests with while the finer grained "Red beds" succeeding 500 feet. These shales represent the Benton found in the deposits. apparent conformity on the Manitou limestone, them, together with the strata of Manitou park division of the Colorado. They are succeeded by but on the southeastern face of the range the were called "Triassic." No reason for the dis­ a limestone complex, the thin layers of which are IGNEOUS ROCKS OTHER THAN GRANITE. characteristically separated by thinner shale seams. latter is more or less eroded, so that the Harding tinction was given by Hayden. [4.] ANCIENT DIKE ROCKS. rests locally on the basal cherty limestone (Cam­ In Garden park the Fountain beds reach a Above this limestone come several hundred feet brian), or even on granite. On the western line, maximum thickness of about 1,000 feet. They of yellowish shales, more or less arenaceous, and Diabase and syenite. The granites and gneisses toward Canyon city, the Harding beds rest on are heavy bedded, with much feldspathic material the two divisions comprise the Niobrara formation of the Colorado and Wet Mountain ranges are cut gneiss, apparently by overlap. The name given derived from the adjacent granite. The con­ as it is characteristically seen at many localities by a great many dikes of diabase and syenite, the formation is that of a stone quarry near Can­ glomerate layers contain many pebbles of hard along the Colorado range, to the north and south. which are not known to penetrate the Cambrian yon city, affording excellent exposures. Algonkian quartzites while a few limestone and The formation is best developed in the valley of or later sediments, and hence probably belong to The Fremont limestone. Succeeding the Hard­ chert pebbles were noted in the lower part of the Oil creek. In Twelve Mile park both the Benton a very ancient period of intrusion. ing sandstone with apparent conformity there series. Dark shales are less prominent than in and the Niobrara seem much diminished in thick­ A great majority of these dikes are of a dense occurs a bluish gray or pinkish dolomite of uneven Manitou park. The Fountain beds rest uncon- ness, and in the locality called The Basin the dark green or black trap rock, a typical diabase. grain, sometimes arenaceous, which gives rise to formably upon the edges of the entire Silurian Dakota is succeeded by limestone with but a few Only in a few observed cases is the grain of the very rough weathered surfaces. It forms the pro­ section in Red ridge, at the upper end of Garden feet of impure shales between. Characteristic rock coarse enough to permit recognition of the tecting cap of the gently inclined mesas at the park, and along the southern end of the Colorado fossils of the formation are found here, but not in augite and plagioclase by the naked eye. The north end of the Garden park bay, and of the range they come in contact with the Harding sand­ abundance. petrographical structure technically called ophitic steeper dip slopes south of West Wilson creek stone. Beyond the eastern line of the Pikes peak The Montana. This division of the Cretaceous is commonly well developed. Some of the dikes and north of Six Mile park. There are often sheet they are usually found to abut against is represented within the limits of the atlas sheet are rich in olivine. small caverns and hollows in the cliff faces of this granite or gneiss. only in Twelve Mile park, where there is a thick­ Far less abundant than diabase are dikes of rock. The thickness of the limestone in Garden No fossils are known in this formation and it is ness of a few hundred feet of characteristic gray syenite. These are usually reddish in color, and park is about 100 feet, but it increases southward, assigned to the Carboniferous from the fact that or yellowish brown arenaceous shales, containing consist of orthoclase, plagioclase, hornblende and and near Canyon city reaches a maximum of 270 in many other parts of Colorado, notably on the an abundance of clay ironstone concretions. It is biotite in variable proportions. A gradation to feet. This is partly through the development of Arkansas river 50 miles westward, there is a great probable that only the Pierre or lower division of diorite is shown by a preponderance of plagioclase an upper and highly fossiliferous member not seen series of similar red sandstones and grits of Car­ the Montana is represented in this park. in some of the dikes. boniferous age, as proved by fossils contained in The dikes of this series are most numerous in in Garden park. EOCENE PERIOD. The Fremont limestone of Garden park is es­ thin limestone strata occurring at various horizons the vicinity of the Arkansas river and are partic­ pecially characterized by the chain coral Halysites in the section. While a greater part of the "Red The Florissant lake beds. The largest post- ularly well exposed in the walls of the Royal catenulatus, and also contains a large invertebrate beds" series east of the Colorado range has been Cretaceous lake basin of the district is that about Gorge and adjoining canyons. One distinct dia­ fauna like that of the upper Trenton of New York. considered "Triassic" no fossil or other definite Florissant. As shown by the map this lake occu­ base dike is exposed in the streets of Cripple Masses of chain coral two feet in diameter are not evidence has as yet been found to show the cor­ pied a long, narrow depression now traversed by Creek. The dikes are usually very narrow and uncommon. rectness of such a conclusion. It is deemed more Twin creek and its southern tributary, Grape creek, the scale of the map does not allow of their rep­ This limestone horizon has not been recognized probable that the lower part at least of these and extended for varying distances up some of the resentation upon it. in other sections of Paleozoic strata along the "Red beds" belong to the Carboniferous, than side gulches. Its length was about 15 miles and The character of many of the diabase dikes is east base of the mountains, nor has its equivalent that the whole complex is Triassic. its width very irregular, but its f ormei area cannot obscured by the paramorphic change of augite into hornblende and in zones of shearing the dike and some of biotite and hornblende. The ground- notably a rock occurring near Altman on Bull George, through Blue mountain, to the neighbor­ rocks are locally altered into amphibolitic or mass is almost equal in amount to the large crys­ mountain, carry large tabular crystals of sanidine, hood of Alnwick and thence south of east through chloritic schists. tals and is very fine grained, but holocrystalline. giving the rock a typical porphyritic structure. the Cripple Creek region. Massive granite also It is plainly a less basic rock than the pyroxene- The bleaching of a thin outer zone by weather­ appears in large bodies to the west and southwest BASIC BKECCIA AND AGGLOMERATE. andesites of the breccia. ing, and a pronounced tabular jointing, are thor­ of this line, but a gneissoid structure either pre­ Occupying about 75 square miles of the west­ Hornblende- and mica-andesites. Under this oughly characteristic features of this rock type. dominates or is locally developed in many places. heading are included many rocks varying greatly The plateau region is generally smooth and ern portion of the district is a dark volcanic SANDSTONE DIKES. breccia or agglomerate made up of several allied in the relative and absolute amounts of hornblende, often densely wooded, but presents a number of A unique feature of the geology of this area is types of basic igneous rocks. It forms a geologic biotite and augite present in more or less distinct bald knobs of massive rock which project above the occurrence of distinct dikes of fine grained, unit by virtue of its mechanical constitution as a crystals. They occur in dikes cutting the augite- the general level and are visible for long distances. massive sandstone in granite. They occur on the bedded aerial formation, building up mountain andesite as well as the basic breccia, and are also Dome rock is a characteristic landmark of this western border of the southern portion of the masses 2,000 feet and more in height upon the found as sheets and irregular masses. type. Manitou park sedimentary basin, and some of the granite plateau. Usually plagioclase, hornblende and biotite are Crystal peak, north of Florissant, is a very largest ones are represented upon the map. The Mechanical constitution. The fragmental for­ prominent in distinct crystals in a predominant noticeable point, in the vicinity of which are many dikes vary from a feiv inches to 300 yards in mation in question has a nearly horizontal bedded dense gray groundmass which may contain quartz coarse veins in the granite, from which huge crys­ width, and are often connected by cross fissures. structure varying in distinctness in different local­ or tridymite. The andesite of the Bare hills and tals of quartz and amazonstone and other feldspars They stand nearly vertical, have a general trend ities. In texture it ranges from fine grained tuffs of the sheet about Cap rock have very few distinct have been obtained, together with many beautiful from north-northwest to south-southeast, and are to irregular and chaotic mixtures of large and crystals of any kind and the dark gray predomi­ crystals of topaz and phenacite. [6.] Raspberry known in this direction, both to the north and mountain, northwest of Pikes peak, is character­ small fragments. Certain layers are fine grained nant groundmass carries much tridymite. east of the area of the map. ized by a porphyritic facies of the coarse granite. and well stratified but as a rule the bedding is ANDESITIC BKECCIA. The material of the dikes is a uniform fine rude and becomes prominent only in large ex­ District adjacent to the Platte canyon. The grained sand, composed almost wholly of worn mountainous area to the northwest of the Eleven posures. The structure is most clearly seen in JBare hills area. The smaller of the two areas quartz particles, with a very little feldspar, indur­ Mile canyon of the Platte river presents a very Saddle mountain, The Castle, and Mclntyre of andesitic breccia and tuff represented upon the ated and colored dull red by flakes of limonite. complicated association of several distinct granite mountain north of West Four Mile creek, whose map, situated in the Bare hills south of High No sandstones of such uniform constitution are types containing many inclusions of Algonkian masses are chiefly made up of this material. park, is characterized by a fine grained, light gray known in the Fountain beds, and no genetic con­ quartzites and schists, and there is also a develop­ The greater part of the formation consists of tuff consisting of very light colored mica- and nection can be made out between the dikes and ment of gneissoid structure from the granite, heavy banks of agglomerate in which large and hornblende-andesite particles, together with vari­ sedimentary rocks. The dikes must be considered which may be clearly seen in the mountains and small fragments are promiscuously mingled. In able amounts of sand and gravel derived from as injections of quicksand into fissures in granite, canyon walls. A most intricate mingling of rock some places the larger fragments are much granite and gneiss. Larger fragments of the same but the source of the sand is unknown. [9.] types characterizes the country south of the Platte rounded and in others they are angular. The rocks are locally abundant. The tuff is soft and for a short distance, and eastward to Blue moun­ fragments represent compact and vesicular rocks crumbles. It is overlain and penetrated by sheets GENERAL GEOLOGY. tain ridge. of various allied types in irregular association. or dikes of dense andesite. It is evident that there Western cental area. The foundation upon There is no evidence that the strata were assorted was here a local center of eruption. DISTRIBUTION OF ROCK FORMATIONS. which the volcanic breccia of this region rests is by water and the constitution of the mass is Cripple Greek district. The principal rock of A glance at the map shows that in general the almost entirely of fine grained, massive, reddish that which is characteristic of accumulations about the Cripple Creek region is an andesitic breccia distribution of the great rock classes corresponds granite characterized by very numerous inclusions great centers of violent and repeated volcanic out­ allied to the basic breccia of the western area in to the development of certain topographic features. of Algonkian quartzites, fibrolitic and micaceous bursts. mechanical constitution, but containing less basic Thus the mass of Pikes peak and the greater part schists, and finely laminated gneisses of question­ The agglomerate is penetrated by numerous varieties of andesite, as far as they can now be of the adjacent plateau are made up of granite and able origin. On the north and east of the vol­ narrow short dikes of compact basalt, and the determined. The extensive decomposition which gneiss. The plateau has been modified, however, canic area the granite forms very smooth park- same rock in local intruded sheets causes benches the rocks about this eruptive center have suffered by large extrusions of igneous rocks, building up like areas as a rule. On the south the forms are in several mountain masses. These sniajl bodies renders their full identification impossible. De­ mountains upon it, mainly through true volcanic more rugged owing to numerous deep canyons. could not be represented upon the map. They tails of the formation are given in the text ac­ activity. Sedimentary beds are now chiefly con­ Gneissic structure appears on certain shear zones are especially abundant in Saddle mountain and companying the special map of the mining dis­ fined to the low ground along the borders of the and at the head of Mac gulch foliated rocks pre­ the Castle. trict. Plains and in Garden park bay, or to small lake dominate. The fine grained granite of High park The greater part of the agglomerate is soft and EHYOLITE. basins on the plateau. The former greater exten­ and vicinity is especially full of fragments of crumbling. An exception to this rule is the hard Rhyolite occurs principally in numerous small sion of some of these formations is indicated by schistose rocks. Tourmaline-bearing veins are bank of dark breccia forming the summit of The remnants of surface flows, and in all these cases facts which will be given. very rarely found in this area. Castle. The dikes and sheets of basalt in certain it is a light colored, felsitic, thinly banded rock, AREAS OF GEANITE AND GNEISS. Southwestern area. The district traversed by areas have protected the soft agglomerate from containing a few small white or glassy crystals of the canyons of Currant, Cottonwood and Tallahas­ erosion. Through decomposition and weathering plagioclase and leaves of biotite, with quartz in a Granite and gneiss constitute the great bulk of see creeks presents predominant gneissoid rocks the complex has usually acquired a characteristic few places. The most common color is ashen the Colorado range throughout its length, but derived from the shearing of fine grained red reddish brown or purplish color. gray, but it is often white or pale pink. their genetic relationships have never been studied granite. There are also dark hornblendic gneisses Petrographical character. The lower part of In the southwest corner of the district on either in detail at any point. They were indicated to­ in slight development, which appear to be derived the agglomerate or breccia is entirely made up of side of Tallahassee creek, beds of rhyolitic tuff gether upon the Hayden map of Colorado as from ancient igneous rocks. In the upper part of dark volcanic rocks belonging to a group on the and breccia occur with surface flows some por­ " Metainorphic granite," and they cannot now be Currant creek there is, however, considerable line between basalt and andesite. They contain tions of which have a banded spherulitic structure. separated on the Pikes peak sheet because of the massive granite. The fine grained granite type pyroxene and olivine in varying amounts but are great complexity of their relations, requiring for prevails in Wilson park, but the rugged mountains never so rich in these constituents as the normal TRACHYTE. their proper understanding and expression long and bounding the park are chiefly of the coarse basalts cutting the breccia in dikes. The olivine To the south of Wicher mountain is a very careful investigation. grained porphyritic granite in which gneissoid is replaced to a large extent in some of the rocks marked group of rounded hills formed of trachyte, Pikes peak. The mass of Pikes peak above structure is very commonly developed. by the substance of undetermined character which and the same rock occurs in several other masses the 10,500-foot level consists of reddish granite of The transitions from the massive porphyritic has been called iddingsite. to the north and west of Cover mountain. The several types, the oldest and principal one being rock to augen-gneiss are most beautifully shown The structures of the rocks of this series vary trachyte is massive, light gray, pinkish or white, the very coarse grained rock named after the peak in the mountain south of Twelve Mile park. greatly. Many are vesicular or scoriaceous while having a few glassy sanidine tablets, numerous in the preceding description. This is penetrated The great quartz ite inclusion of Wilson park others are dense. The groundmass is prominent smaller plagioclase crystals and hexagonal leaves by numerous dikes and irregular bodies of finer forms one of the most noticeable features of this in all varieties and granular types have not been of biotite in a strongly predominant groundmass grained varieties, especially in the upper pyramid portion of the area. observed. which possesses the typical trachytic structure, of the peak, above 13,000 feet. Vicinity of Cripple Creek. Cripple Creek lies In the upper part of the complex more distinctly being composed of feldspar tablets and inicrolites, In the granite mass are carved several glacial on the line where the coarse granite of the Pikes andesitic types appear in which olivine is replaced with very little quartz. These trachytes approach amphitheatres, the largest being on the west and peak type is cut by many arms of fine grained by hypersthene, and some normal augite-andesites the rhyolites in having some excess of silica but southwest. To the north and east the peak pre­ granite of the western area. The canyons carved are found. Fragments of trachyte and of horn- in structure they contrast strongly with the rhyo­ sents very rugged slopes with smaller amphi­ by the eastern tributaries of Oil creek present blende-andesite are also mingled with the basic lites of the region. In some cases the trachyte theatres. On all the gentler slopes of the upper these two granite types in extremely complicated rocks in the upper beds of Mclntyre mountain, is brecciated. Its fragments are also found part of the peak the disintegration of the granite association. For the most part the rock is massive and in the district south of High creek. mingled with hornblende-andesite in the upper affords sufficient soil to support a beautiful alpine or but indistinctly gneissoid, yet local shear zones In the mesa of the southwestern corner of the part of the basic breccia. flora. expose finely laminated rock. Both granites are district are several thin flows of olivine-bearing While no distinct gneissoid structure has been characterized by many inclusions of fibrolitic and PHONOLITE. andesite similar to the fragments of some portions seen in any part of the Pikes peak mass there is micaceous quartzites. To the east of Cripple of the agglomerate. The region about Cripple Creek is specially sometimes a decided sheeting of the rocks by Creek, on Middle Beaver creek, the transition characterized by many masses of the rare igneous MASSIVE ANDESITE. vertical, parallel joints, and this gives rise to the from granite to gneiss is most clearly shown in rock, phonolite, elsewhere known in the United peculiar pinnacled and turreted forms called The many exposures on and near the Colorado Springs The rocks included under the general term States only in the Black hills of Dakota. Phono­ Crags, at the northwestern extremity of the moun­ road. andesite upon the map are of many mineralogical lite is a rock allied to trachyte but characterized tain. Similar projecting cliffs are seen at the Southern district. The plateau extending south­ varieties and occur in great abundance as dikes by the presence of nepheline in addition to alkali- ends of some of the southern ridges. ward from Cripple Creek is generally character­ cutting the basic breccia or as sheets resting upon feldspar, a result of its richness in soda and its low The granite plateau. The coarse grained Pikes ized by coarse grained granite and gneissoid forms it. But some of the masses may be older than percentage of silica. peak granite forms the greater part of the plateau, derived from it. A fine grained massive granite, the breccia, for the relationship is not always clear. The phonolites of this district are, when fresh, reaching west and north from the peak for several however, is very prominent in the region cut by These andesites may be divided into two classes, dense greenish gray rocks, often with a sub-vitre­ miles. Northward this granite type extends far the deep canyon of East Beaver creek. In Eight those characterized by augite, and those contain­ ous lustre. They are usually somewhat decom­ beyond the limits of this sheet and it is known in Mile canyon are many beautiful exposures of ing hornblende and mica. posed, however, and are then dull, yellowish large masses at Devil's Head on Platte mountain, gneissoid rocks, showing their relationship to the A.ugite-andesite. -This type forms a group of brown, straw-colored, pink or white. Some of the and in the lower canyon of the Platte river, but massive granite, and on the lower slopes adjacent massive rounded hills at the head of West Four rocks of the region have no distinct crystals visi­ whether it occurs as a continuous body or in to the sedimentary rocks finely laminated gneisses Mile creek and constitutes the main mass of Cover ble to the naked eye; others have small glassy separated areas is as yet unknown. The general are very common. Their strike is entirely dis­ mountain. The rock is compact, and porphyritic, tablets of sanidine and dark green prisms or grains western limit of the massive rock is an irregular cordant with that of the sedimentary rocks rest­ with abundant crystals of plagioclase and augite, of segirine, a soda-bearing pyroxene; and a few, line extending from the Platte river at Lake ing upon them. Several large inclusions of Pikes Peak 3. Algonkian quartzites are shown in the granites amounts to nearly 1,000 feet, but greatly dimin­ only in small perfectly rounded pebbles, affording East of Little Pisgah peak there is a large irregu­ and gneisses of this district, the most prominent ishes southward to the vicinity of Millsap creek, evidence of a great amount of attrition. There is lar neck of phonolite, cutting the granite in the ones being in Cooper mountain, and in Eight Mile where it passes into a fold. To the north of Wil­ at present a difference of 500 feet in elevation be­ rugged cliffs facing Wilson creek. A great many canyon at McCourt camp. son creek within the semicircular curve in the tween the floor of High park and the summit of dikes of phonolite are found in granite on all sides course of this fault there has been a slight over- Red ridge. of the volcanic center. Traces of rhyolitic tuff AREAS OF SEDIMENTARY ROCKS. thrust movement of the granite upon the sedi­ AREAS OF VOLCANIC ROCKS. and breccia found at a few points indicate the al­ mentary beds. Profile sections DD and EE of the most complete destruction of a formation of this Southeastern area. In the southeastern corner Western central area. The largest area of vol­ structure section sheet cross Garden park bay. character which may have been quite extensive. of the district, where the sedimentary formations canic rocks in the district represents the eastern Scattered remnants of rhyolite. The geologic of the plains are upturned at the base of the Twelve Mile park. In Twelve Mile park and ex­ extremity of a volcanic formation which occupies map shows a large number of very small patches granite mountain mass, the characteristic foot-hill tending over the little divide into West Eight the greater part of the elevated country between of rhyolite, most numerous in the vicinity of the structure is very clearly illustrated. The outermost Mile park is an isolated area of Mesozoic strata in South park and the Arkansas river. The princi­ formation here exposed is the Dakota sandstone a synclinal basin. The Morrison, Dakota, Colorado Florissant lake, but also noticed as far south as the pal formation in this volcanic complex is a dark, eastern ridges of the Bare hills. The rock of all forming mesas sloping gently to the south but and Montana formations are present, but on the basic breccia and agglomerate with numerous in­ of these patches indicates a finely banded surface presenting a cliff front to the northwest and southwestern side the Colorado shales apparently tercalated basalt sheets and dikes. This agglomer­ flow of no great thickness. The rock is very uni­ toward Beaver creek, which cuts through it. The overlap the lower formations along a shore line. ate accumulated on an irregular floor of granite form in appearance throughout the region, but the gentle dip of the Dakota causes it to form mesas Near Bumback Springs a small remnant of Mani­ and gneiss, as proved by the local projection of remnants found occur at many different elevations in the districts of the Colorado Springs, Pueblo tou limestone is found dipping beneath the granite through it and the occurrence of the ag­ and Canyon city sheets. The Morrison formation Morrison beds. All this area was once directly entirely independent of present topography. In glomerate in valleys and hollows. The basic how far the differences of level observed have occurs in a narrow zone below the Dakota cliff connected with the Mesozoic of Garden park bay breccia forms mountains and mesas, the largest been produced by faults undetected in the granite and in the valley of Beaver creek. Between the over the low divide, and also with the strata now masses lying, however, west of the area mapped. it is impossible to say, but the fact that the rhyolite Morrison and the base of the mountain is a broad found about Parkdale in the Arkansas valley to North of Four Mile creek are several mountains zone underlain by the crumbling grits of the Foun­ the south. capping of Red ridge bears upon it a conglomer­ composed of the agglomerate with capping sheets ate apparently identical with the High park con­ tain beds, which by their disintegration and ready Hemnants upon the plateau. Near the southern of andesite. To the south the agglomerate forms glomerate, indicates a dislocation between these erosion produce little park areas. The dip of end of the Colorado range several small remnants the main part of Wicher mountain, and in its points of nearly 500 feet, and it is quite probable these beds are 10° to 15°, except for the lower of Silurian limestone have been found in nearly further extension produces the large dissected that many other differences in elevation of rhyo­ strata which acquire a dip of 30° or more, and run horizontal position, at elevations up to something mesas on either side of West Wilson creek. The lite remnants are due to the same cause. some distance up on the foot-hill ridges. A rather more than 9,000 feet. The highest and most large intercalated andesite sheet has been an im­ narrow band of the Harding and Manitou forma­ northerly of these remnants is on the ridge east of portant element in the preservation of these mesas. STRUCTURAL DEVELOPMENT tions appears below the Fountain grits, and ex­ Lower Beaver park. Another appears one mile Massive andesite and trachyte also form hills OF THE REGION. tends back on the ridges to variable distances. southeast of Nipple mountain, while several and mountains within this general area. These To the west of Eight Mile canyon the Silurian smaller ones occur on the southern spurs of Cooper rocks are more recent than the earliest portions of No approximately complete sketch of the geolog­ rocks reach far up on the mountain slopes, ap­ mountain. The largest patch appears on an un­ the great breccia formation and are distinctly ical history of this region can as yet be written, parently because of the protecting sheet of Fre- named mountain east of Eight Mile canyon. older than the upper part of the fragmental de­ owing to the reconnoissance character of the ob­ mont limestone which is here present above the In the last named remnant the Harding sand­ posits. Dikes of these rocks penetrate the lower servations thus far made, and the obscurity of the Harding sandstone. stone is present with a very thin layer of Manitou part of the breccia in great abundance. Rhyolite evidence concerning some of the most important Crossing the lower part of Eight Mile canyon is limestone below it, and in all other cases it is occurs in small masses associated with the other geological periods. The data that have been pre­ an overthrust fault with a northeast-southwest usually the cherty lower layer of the Manitou volcanics, apparently in remnants of an extensive sented, however, throw new light upon the history trend and steep dip which passes into a fold at which is preserved. Similar remnants found be­ but thin surface flow. There is a local center of of certain periods, and a summary review of the either end, but has produced a considerable dislo­ neath the Morrison beds near Bumback Springs andesitic eruption on the south side of Four Mile succession of events as thus indicated will be cation in its central part, bringing up the crystal­ and on the south side of Wilson park, show that creek opposite Truro. The rocks of this large given. line rocks on the southeastern side. the Silurian ocean of the Manitou and perhaps of volcanic region are as a rule very fresh. Age of the granites and gneisses. The granites Garden park bay. Wrapping around the end other epochs covered considerable territory on High park. Near the center of the High park and gneisses of the Rocky mountains have always of the Colorado range the sedimentary formations either side of Garden Park bay. These remnants depression are some prominent hills composed of a been considered to be a part of the Archean, the extend northward into an old bay the boundaries have been isolated by erosion in the arch of the rather fine grained tuff and agglomerate chiefly of oldest known complex of rocks, whether deemed of which have varied greatly at different times. monoclinal fold, probably during the interval be­ andesitic material. Southward from these hills to be plutonic eruptives or of metamorphic origin. The principal element in the present structure of tween the Millsap and Fountain epochs of the the even floor of the park is covered by a thin But a remarkable feature of the area of the Pikes the sedimentary formations of this bay is a flat Carboniferous period. rhyolite flow, upon which the High Park lake beds peak sheet, now observed for the first time, is the syncline whose axis pitches at a low angle in a West of Oil creek a patch of Dakota sandstone were deposited. The relative age of the volcanic occurrence in the main granitic masses of an southerly direction. At the mouth of the bay occurs on the south side of Wilson park; two rocks here exposed was not positively determined. enormous number of included fragments of are seen the Colorado and Dakota rocks of the patches of Morrison and Dakota occur on West But the absence of andesitic debris in the sedi­ quartzite and of schists derived from them. The Cretaceous period, the latter forming a regular dip Wilson creek southeast of Cap rock; in and near ments of the High park lake seems to show that purer quartzites are plainly indurated sandstones, slope on either side of Oil creek, bounded by cliffs High park are several small remnants of the Mor­ the andesitic tuffs are younger than the rhyolite. necessarily older than the granites which include which are well expressed upon the map. Near the rison beds; and in The Basin, below the volcanic In the hill on the eastern side of the park the lake them. From considerations presented elsewhere border of the map on both sides of this syncline breccia, is a well characterized exposure of Dakota beds are found between flows of rhyolite and these ancient sediments have been referred to the the Dakota assumes a steeper dip, forming charac­ and Colorado (Cretaceous) strata. All of these phonolite. Algonkian period. The granites cutting these teristic hogback ridges, one extending southward remnants occur either in park depressions or where The Bare hills. Southward from High park strata are then either of Algonkian age or of early to Canyon city, and the other curving eastward they have been protected by overlying volcanic is a group of bare, grassy hills upon the site of a Cambrian, and it is deemed most in harmony with to a connection with the mesa of the southeast rocks. They seem to represent deposits in hollows vent of andesitic eruption. The earliest outburst the other facts in the case to refer the granite erup­ corner. Below the Dakota the Morrison formation of a sea whose floor was gradually sinking. at this point produced a fine grained, light colored tions to the later Algonkian period. With such extends a long distance into the old bay, with Manitou park basin. In the northeastern tuff full of fragments of granite. Penetrating an age assigned to the granites the dynamic move­ remnants of the Dakota here and there upon it. corner of the district, near the head of Fountain this tuff are several necks and dikes of dense ment which produced gneisses out of them may In this formation near Oil creek are the famous creek, occurs the southern end of the Manitou park hornblende-mica-andesite. The surface masses well be considered indentical with that which pre­ Dinosaur beds from which great numbers of type, basin of Silurian and Carboniferous rocks. The erupted through these channels built up the higher ceded the Cambrian. It is known that the gneissic specimens have been obtained. Oil has been basin structure now seen is apparently due entire­ portions of the hills resting upon the tuff or upon structure in question was produced before the found in small quantity in the Morrison beds not ly to folding, and the strata are supposed to have the outlying granite. period of the upper Cambrian, during which time far below the Dakota, on the eastern side of Oil been connected with the main areas to the east. Southwestern area. In the extreme southwest­ sediments were deposited upon these gneisses in creek. On the eastern edge of this basin the Manitou ern corner of the district is a narrow mesa which the Colorado range. The Fountain grits form the floor of Garden limestone appears as a narrow band in vertical is capped by several thin sheets of olivine-bearing Pre-Paleozoic land areas. The fragments of park proper and extend northward until cut off position. Above it the Fountain grits possess a andesite which rest upon rhyolitic breccia and tuff, quartzite, schist and gneiss included in the granite by a transverse fault. The northern part of the greatly diminished dip toward the west and on the beneath which on the northern side are remnants must be regarded as representing the oldest known Garden park bay contains three Silurian forma­ eastern line abut against the granite. Whether of a dark basic breccia seemingly equivalent with rocks of this portion of the Colorado range. But tions exposed in southerly dipping mesas, cut by this western contact represents a fault or an that to the north. On the northern side of Talla- it is impossible from present knowledge even ap­ canyons affording excellent exposures. In Red ancient shore line is not definitely known. The hassee creek rhyolite and basic breccia seem to al­ proximately to define the continental areas of the ridge, at the extreme northern limit of the bay, a basin ends to the south on account of the north­ ternate. Both of these isolated patches belong to period of sedimentation, or the extent of the de­ remnant of Fountain beds rests nearly horizontally erly pitch of the synclinal axis. The structure is the great western volcanic district the margins of posits. The enormous granite masses which broke upon the edges of the Silurian formations. The shown in section AA of the structure section which approach very near the border of the map. into and through these oldest formations doubt­ preservation of the Fountain beds is due to a sheet. Cripple Greek district. The group of hills con­ less formed extensive land areas, but it seems rhyolite sheet above them. Eocene and Neocene lake basins. The largest of taining the mines of the Cripple Creek region are probable that the great dynamic movements which The present limitations of the sedimentary for­ the post-Cretaceous lake basins, that about Florris- chiefly made up of a much decomposed andesitic transformed so large a part of these massive mations of Garden park bay are chiefly determined sant, has been quite fully described in discussing tuff, breccia, and agglomerate formation, with granites into banded gneisses were the ones which by a complicated system of faults. These have the character of the sediments. It does not appear to small bodies of massive andesite, and penetrated gave outline to the continents about which the lowered the bay area with respect to the granite have been at any time much larger than is indicated by numerous dikes of phonolite. Detailed de­ upper Cambrian and Silurian strata were de­ mountains on either side. They are situated by the strata now preserved. The Alnwick lake scriptions of the central portion of this region ac­ posited. Much further investigation is necessary principally at the foot of steep monoclinal folds on in the valley of Oil creek appears also to have company the special map of this folio. Beyond to determine how large a part of the gneisses in either side of the syncline. Variations in strike of been limited by topography very much like that the borders of the special map there are, however, other portions of the Rocky mountains has been the steeper inclined beds on the mountain sides of the present day. The lake of High park, how­ many phonolite masses which are distinctly formed from granites contemporary in origin with have brought them against the fault in several ever, had an extension to the southeast as shown grouped about this center, and are to be considered those of the Pikes peak district. places in such a way that the formations have by the remnant of its lowest conglomerate found as belonging to it. The main structural axis of this portion of the been successively sheared off in the manner repre­ upon the rhyolite sheet capping Red ridge. The outlying phonolite masses range from a Rocky mountains has a trend north-northwest sented upon the map. The principal faults trend There is no evidence concerning its former limita­ point on the slopes of Pikes peak itself, seven and it is parallel to this general direction that the nearly north and south, but several smaller trans­ tion in this direction. Apparently this lake must miles northeast of Bull mountain, to Nipple moun­ banded structure of the gneisses has been de­ verse faults have greatly complicated the structure. have had a considerable body of water, for the tain on the south and High park on the west. veloped. There are many minor deviations from The great fault east of Helena canyon is most chief constituent of its conglomerate is the ex­ Nearly all of the larger bodies seem to be surface this rule, but the broad correspondence in struct­ clearly marked. Its throw near Wilson creek tremely hard Algonkian quartzite which occurs masses from sources immediately below them. ures is nevertheless plain. From the upper Cambrian to the Eocene it seems probable that tion of the periods of elevation and erosion which which deposited a great mass of material at the Hayden, geologist in charge, IT. S. Geol. and the oceanic shore line along the eastern base of the preceded this subsidence are not indicated in the mouth of its canyon. This has apparently been Geog. Surveys of the Territories. Department of Colorado range remained very near the present region of the map, but if the Fountain grits were greatly modified by rearrangement and disintegra­ the Interior, Washington, 1877. The Pikes peak line of contact of the sedimentary formations, ex­ deposited during the later Carboniferous, there is tion of the granite boulders. Probably much evi­ district is included in Sheet XIII. cept in certain epochs. no record here of the passage of time to the middle dence of glaciation has been destroyed by the sur­ 2. A. C. Peale. Annual Report of the Geol. Early Paleozoic movements. The overlapping of the succeeding period, which is elsewhere rep­ face decay of the granite. and Geog. Surveys of the Territories for 1873. of later formations conceals the older Paleozoic de­ resented by thick sediments. These have been as­ In the vicinity of Divide and Summit several The region about Manitou Springs, Manitou park, posits except where they have been exposed in a signed by other geologists to the Permo-Carboni- square miles of smooth grassy country are under­ and the northern portion of the Pikes peak dis­ few isolated localities by some special structural ferous and Triassic during which thick sediments lain by a superficial formation which is apparently trict are described on pages 193 to 212. disturbance and subsequent erosion. It is how­ accumulated elsewhere in the Rocky mountain glacial drift, consisting of small rounded bowlders 3. F.N.Endlich. Ibid. A description of the ever to be assumed that all of the known forma­ region. If deposits were formed during these and gravel. Phonolite and various other eruptive southern part of the Pikes peak district is con­ tions had at least a considerable extension along periods in this region they were eroded before the rocks of the region are represented among these tained on pages 305 to 322. the eastern base of the Colorado range. The ex­ subsidence preceding the Morrison. bowlders. Very similar material also appears on 4. F. V. Hayden. Annual Report of the U. S. posures in Manitou park and on the plateau to the The district of the Pikes peak sheet presents no the plateau-like crest of the Colorado range, in the Geol. and Geog. Survey of the Territories for south of Pikes peak show that the late Cambrian evidence concerning changes during the long extreme northeastern corner of the mapped area. 1874. A general description of the sedimentary and early Silurian oceans covered a part of what Cretaceous period, except those which are common The origin of this material and its distribution be­ formations recognized along the foot hills, with is now mountainous territory. to the general Rocky mountain region. yond the map borders were not ascertained. a map of the vicinity of Manitou Springs and Orographic movements of probably minor im­ Post-Cretaceous movement. The upturning of Disintegration of the Pikes peals granite. A references to local geology, will be found on portance during lower Silurian times are proved the sedimentary formations in a narrow zone along marked feature of the coarse grained Pikes peak pages 40 to 46. by unconformities between the Silurian deposits the foot hills of both the Colorado and Wet moun­ granite is the readiness with which it disintegrates 5. Samuel H. Scudder. The Tertiary Lake of Garden park bay and vicinity. The chief of tain ranges has probably been a progressive move­ under the action of atmospheric agencies. Many basin at Florrissant, Colorado, etc. Bulletin U. these appears to have been between the Manitou ment, interrupted at intervals by disturbances slopes of the peak proper, and large areas of the S. Geol. and Geog. Survey of the Territories, Vol. and Harding periods; the Harding sandstone in whose characteristics are imperfectly recorded in adjacent plateau are covered by coarse angular VI, No. 2, pp, 279-300, 1881. Gives a general certain places resting upon granite through erosion the unconformities described. But from the evi­ gravel, resulting from the disintegration of the sketch of the Florissant basin, with lithological of the earlier strata. dence in the Denver region it is known that a granite in place. This gives rise to gentle and descriptions of the tuffs and a statement concern­ Between the lower Silurian (Ordovician) and movement of special intensity took place at the end rounded forms except where erosion has had op­ ing the fossil fauna and flora. lower Carboniferous periods there must have been of the coal-bearing Laramie (Cretaceous) epoch and portunity to remove the loose material. 6. Whitman Cross and W. F. Hillebrand. Con­ a time of non-deposition and erosion, some clear another followed some time during a subsequent Erosion. The topography of the southern por­ tributions to the Mineralogy of the Rocky Moun­ evidence of which is found in an undoubted un­ period, by which the post-Laramie (Cretaceous) for­ tion of the district has been greatly modified by tains. Bulletin U. S. Geological Survey, No. 20, conformity between the Millsap (Carboniferous) mations were also steeply upturned, corresponding erosion during recent epochs. Thus the southern 1885. Minerals from the neighborhood of Pikes limestone and the Fremont (Silurian) limestone. in position to the older formations. From the end of the Colorado range has had its plateau peak, pp. 40-74. Describes the cryolite of St. Pe­ Carboniferous movements. The extent and char­ structure found in Huerfano park at the south end character almost obliterated by the erosion of ters dome and its alteration products, and also acter of the deposits laid down in this region in of the Wet mountains it is known that a further many deep canyons by the tributaries of Oil, topaz, phenacite, zircon, etc. from veins in granite. the lower Carboniferous period are practically movement of this character took place after the Eight Mile and Beaver creeks. The plateau 7. Samuel H. Scudder. Tertiary Insects of unknown. The thin, locally preserved remnants Bridger (Eocene) epoch. But as no strata later than country west of Pikes peak has on the other hand North America, U. S. Geol. and Geog. Survey of of the Millsap limestone are all that remain of the Montana (Cretaceous) formations are exposed suffered comparatively little erosion since the the Territories. Monograph XIII, 1890. The what may have been a thick formation. Of the near the southern end of the Colorado range it is time of the post-Cretaceous lake basins and the greater part of the insects described came from Fountain beds there was, however, uplift, fold­ impossible definitely to connect the last important filling of the valleys with volcanic material. the Florissant lake beds, and there is a description ing and erosion, continuing through an interval of disturbances of the Pikes peak district with any The southwestern portion of the district and of the locality similar to that of 5. unknown duration. If the Fountain grits be as­ of these great orographic movements. Thus the the region traversed by the Arkansas, a short dis­ 8. C. D. Walcott. Preliminary notes on the signed to the upper Carboniferous the preceding upturning in which the Cretaceous strata have tance further south, exhibit many remarkable discovery of a vertebrate fauna in Silurian interval embraced very probably the middle Car­ taken part may correspond to the post-Laramie or peculiarities in the courses of deep canyons in (Ordovician) strata. Bulletin Geological Society boniferous, and was correspondingly longer if the to some distinctly later movement. The faults of relation to the physical character of the rocks in of America. Vol. 3, pp. 153-172, 1892. This grits belong to any later period. There is no Garden park bay are probably still later than the which they have been eroded. The soft sediment­ paper contains a description of the ichthyic evidence to indicate that the known Fountain beds folding. ary rocks of the Cretaceous bay do not seem to fauna of the Harding sandstone, with prelimi­ conceal by overlapping any earlier strata of the PLEISTOCENE GEOLOGY. have determined the courses of any of the larger nary lists of invertebrates in the Harding, Fre­ same general period of sedimentation. Glaciation. Evidence that local glaciers once streams in this region. mont, and Millsap formations, and notes on the Movement preceding the Morrison epoch. The existed on the upper slopes of Pikes peak is found geology of the region between Canyon city and presence of Morrison and Cretaceous remnants in moraines, more or less rearranged, occurring es­ LITERATURE. Garden park. upon granite and gneiss in the western part of the pecially on the eastern and southern slopes of the The most important publications on the geology 9. Whitman Cross. Intrusive sandstone dikes Pikes peak district proves that prior to the Morri­ peak at about 10,000 feet elevation. The most of the Pikes peak district or its vicinity are given in granite. Bulletin Geological Society of son epoch there began a great subsidence which noteworthy morainal accumulation of the region in the following list. References to this list are America. Vol. 5, 1894, pp. 225-230. continued until the latter part of the Cretaceous, indicated by figures in brackets in the preceding embraced by the map is that east of Trachyte WHITMAN CROSS, admitting oceanic waters to the west of the mountain. The branch of Beaver creek which text. Colorado range and apparently establishing a con­ rises in the amphitheatre south of the summit of 1. Geological and Geographical Atlas of Colo­ Geologist. nection with South park. The extent and dura- Pikes peak was evidently occupied by a glacier, rado and portions of adjacent territory, by F. V. June, 1894. Pikes Peak 5. .I L

DESCRIPTION OF THE CRIPPLE CREEK SPECIAL MAP.

GENERAL GEOLOGY. matic crystals of apatite, which are often larger shown in nearly fresh condition in the Elkton­ and breccias of the northern and eastern portions than any other constituent of the rock Raven dike, and in the Black Diamond mine on of the central volcanic area rest upon a surface The field work upon the Cripple Creek special The second andesitic variety occurs in dikes Battle Mountain. The Moose, Ben Harrison, and of granite whose topography must be quite as map was done in September, October, and cutting the breccia, especially in Anaconda Ridge Anna Lee dikes are of nepheline-basalt, very much irregular as the surface of to-day. This is shown N6vember, 1894, after the publication of the and Poverty Gulch. The rock is an augite-ande­ decomposed, and locally impregnated with ore. by the course of the boundary line of the vol­ Pikes Peak sheet. As the scale of the special site with some hornblende and mica, and has a Many other short dikes of Bull and Raven hills canics, and by the islands of granite and schist map is larger the geological details "represented denser groundmass than the earlier type. An belong to one or the other of these basaltic types. which project through the tuff and breccia. The upon it are more complex in character, differing andesite rich in mica occurs in dikes in Battle In their decomposed. state these dike rocks are isolated areas of tuff in Mineral Hill and Rhyo· greatly from the simple outlines of the atlas sheet. Mountain, but is not represented on the map. usually very soft, greenish in color, and often show lite Mountain also illustrate this relation. The outline of the central volcanic area is practic­ Phonolite.-The specially characteristic rock of a straw-yellow mixture of decomposition products From near Anaconda to Victor the contact ally unchanged, but the formation within it has the region is phonolite. It occurs in numerous in place of the augite prisms of the original plane is so steep in several places as to suggest been subdivided and several rock varieties haYe narrow dikes, both within and without the main basalt. Only a few of the best exposed nepheline­ that actual vents of the volcano are directly adja­ been distinguished. Outside the volcanic center volcanic area, and is the only one of the volcanic basalt dikes are represented upon the map. cent, and other evidence points to the same con· the schist inclusions in granite have been indi­ types having such a distribution. It also occurs Tuff and breccia.-The fragmental rocks of the elusion. 'The granite near these steep contact cated, and also a few other formations not shown in several isolated bodies capping granite hills or central volcanic area, which are cut by all of the planes, especially at Anaconda and on the ridge upon the atlas sheet. The area covered by the mountains for some miles on all sides of the massive rocks described except the earliest ande­ south o£ Arequa Gulch, is very much shattered special map is about 38 square miles. center, as in Trachyte, Big Bull, Cow, and Nipple site, consist of sma1l fragments of andesite, phono­ in a most irregular manner, as well as traversed mountains. These masses are thought to be rem­ lite, and granite. The predominant constituent by the usual fissure systems. The granite island IN'rRODUOTORY SKETCH. nants of large inclined dikes in granite, similar to is andesite, with phonolite locally abundant, and of Ironclad and Bull hills is also very much The central portion of the area mapped Is a those shown upon the map in the territory just granite very subordinate, often confined to micro­ broken up. A natural cause for this condition is typical volcanic complex. It consists of pre- ·west of the volcanic center. This origin is further scopic grains. In texture these rocks vary from to be found in the earthquake shocks attending dominant fragmental materials-tuff and breccia suggested by the phonolite bodies of Grouse and fine, even-grained tuffs, composed of sand or gravel the explosive eruptions of the volcano. -with numerous dikes and irregular intrusive Straub mountains, which are clearly lateral intru. particles, to a breccia made up of small angular Brecciation of rock in plaoe.-Many small bodies bodies of massive rocks. This part is naturally sions into the High Park lake-beds, near the fragments, few over 1 inch in diameter. Very of massive volcanic rock in the central area the most complicated and interes-ting geologic- granite surface. No surface flows of phonolite large fragments do not ·occur. The most abun­ correspond in their shattered condition to the ally, and it is also of the greatest economic import- are now identifiable. dant modification contains a few comparatively granite of the contact zone. This is illustrated ance, because the gold deposits are there most Phonolite was a product of several epochs of large fragments in a gravelly matrix, a form in Battle Mountain, Raven Hill, and Bull · numerous. eruption, for a part of the breccia contains phono- which may be called tuff-breccia. Hill. Many dikes are so broken up that the mass Surrounding this central area is granite, the lite fragments, and this breccia is cut by phono­ The greater part of the tuff and breccia is is really a breccia, although the dislocation may principal rock, penetrated by dikes of certain of lite dikes. The dikes are also of several epochs. without distinct bedded structure, but occasion· have been slight. The shock which shattered the the volcanic rocks. Remnants of tuff and breccia The phonolite consists of alkali feldspars, ally a bedding is visible. Owing to the exten· massive rock doubtless affected also the loose frag· also occur, and there are a few subordinate for· nepheline, sodalite, nosean, and pyroxene which sive decomposition to which the rocks of the mental materials and destroyed much of the bed­ mations which are not directly connected in is in great part oogirine .. Accessory minerals are central. area have been subjected the bleached ded structure which may have existed in the tuff origin with the volcanic center. The High Park sometimes present, the most notable ones being and indurated tuffs are in many places distinguish­ and breccia of the central area. lake-beds and the associated rhyolite of Grouse lovenite and a peculiar blue amphibole. The able from massive rocks only by the closest Relationships of the massive rocks.-The ande­ Mountain are the principal of these formations. smaller dikes are dense, of greenish-gray color, scrutiny. Tuffs retaining in some degree their site of Battle and Big Bull mountains is certainly The study of the district has led to the conclu- and have a pronounced fissile or schistose struct­ original dark colors and loose texture are found on older than the tuffs which surround or overlie sion that there was once a true volcano at this ure, due to the arrangement of the predominant the slopes of Bull Cliff and Battle and Big Bull the patches now seen, for those tuffs are clearly center of eruption. It was probably small in scales or microlites of feldspar parallel to the dike mountains, especially near the isolated patches of made up largely of that same andesitic type. The comparison with the one west of it, but it exhib- walls. A few glassy sanidine tablets give a more massive andesite, and in ·these places the frag­ other massive rocks cut the fragmentals as dikes ited · a very complete cycle of phenomena char- or less distinct porphyritic structure to many ments of the breccia can be seen to be identical or necks, but are not shown in sufficiently numer­ acteristic of volcanic vents. Owing to the masses. The phonolite of Grouse Mountain and in character with the massive rock near by. ous masses to determine with certainty the extreme decomposition suffered by many of the of some smaller bodies is porphyritic through the Granite occurs in the tuff-breccia most abun­ sequence in all cases. Phonolite appears to have rocks under the action of gases and thermal unusual development of nepheline in numerous dantly near the boundary line. Phonolite is been the only rock erupted in several periods. waters many features are at first difficult of macroscopic, reddish crystals. Analcite occurs in prominent in the breccia of Anaconda Ridge, The nepheline-syenite body sends off arms recognition. · drusy cavities in certain places. Raven Hill, and in the space between Battle which cut one of the masses of trachytic phono­ Trachytic phonolite.-The large mass of Bull Mountain and Bull Cliff. lite above the "Legal Tender" mine. But all the ROCK FORMATIONS. Hill, and some smaller ones in or near Bull Cliff, Rhyolite.-In Grouse Mountain are isolated rocks except the andesite and basalt are closely Granite and gneiss.-The coarse-grained granite belong to a rock closely allied to the ordinary patches of a banded, pinkish or grayish rhyolite, allied, being very rich in alkalies and poor in lime of the Pi'kes Peak type prevails in the district, phonolite but deserving to be distinguished from associated with the High Park beds. This rhyo· and magnesia, and constitute ·one group character­ except to the west of Cripple Creek, where a it by the smaller amount of nepheline it contains lite contains crystals of sanidine, quartz, and bio­ izing the middle period o£ the volcano. The finer-grained type occurs. Fine red granite dikes and by its structure. There are many stout feld- tite, in a dense groundmass which is some-times nepheline-syenite occurrence is of much import­ \ abound throughout the granite area, and coarse spar crystals in this rock, and it is not laminated. microspherulitic, though usually crypto-crystalline ance as indicating that at the time of its intru­ pegmatite dikes are occasionally found. Gneissic In its prevalent decomposed condition it bears with more or less pronounced fluidal structure. sion the volcanic mountain was large enough to structure is locally developed in the granites, but little resemblance to the normal phonolite, though The rock is like that represented on the Pikes secure for this magma conditions of cooling suita­ neither this structural change nor the distribu­ the fresh rocks of the two types are nearly iden. Peak sheet as widely scattered over the adjoining ble for the production of the granular structure. tion of the granitic varieties could be shown on tical in chemical composition. Sodalite and country north and west of Grouse Mountain, and It is also probable that the mass lies within, or the map, owing. to the limited time available for nosean are as abundant as in the other type. there is no reason to believe that this rhyolite in close proximity to, the central conduit of the the investigation. NepheUne-syenite.-A single mass of this rock was a product of the Cripple Creek volcano. volcano. Schist.-The numerous small areas designated occurs at the south base of Bull Hill. It possesses High Park lake-beds.-ln Grouse and Straub Rock decomposition.-The rocks of almost the schist are not so clearly metamorphosed Algon­ nearly the same chemical and mineralogical com­ mountains is a rudely bedded grit or coarse sand­ entire mass of the central volcanic area and of a kian strata as are many in the adjoining district position as the phonolite, but has less nepheline, .stone composed of granite gravel with some worn large area adjoining on the northwest are very to the west, but they are plainly included masses sodalite, and nosean, and a primary green horn­ pebbles of granitic and schistose rocks and a much decomposed. The prevalent form of this in the granite, and hence to be considered older blende is associatedwith the augite. The rock is smaller number of pebbles of hard, bluish quartz. decomposition is a bleaching by removal of iron­ than that rock. Most of these schistose rocks are pearl-gray in color, with a fine-grained granular ite, derived from fragments of Algonkian quartz. bearing minerals, and a kaolinization or musco­ silvery muscovite-quartz-schists, with fibrolite in structure, excepting on the periphery, where it ite included in granite, described in the text of vitization of the feldspathic constituents. It is many eases. Some are doubtless altered gneisses, becomes porphyritic. The presence of this granu­ the Pikes Peak sheet. The grits are reddish in reasonable to assume that both gaseous and aque­ while others are metamorphosed Algonkian sedi­ lar equivalent of phonolite in the heart of the color, loosely consolidated, and resemble the ous agents were active in producing this decom­ mentary rocks. Those near the volcanic area are volcanic district suggests more definitely than Fountain formation (Carboniferous). On the position, inasmuch as the phonolite, the principal· much kaolinized. Small granitic veins or dikes anything else the site of the actual vent of the ridge south of Grouse Mountain these grits locally rock of the volcano, contains fluorine, chlorine, and penetrate the schist. volcano. rest upon rhyolite. This relationship is so similar sulphuric acid, and it is scarcely conceivable that Diabase.-Several diabase dikes in granite are Syenite-porphyry.-On the southeast shoulder to that between the rhyofite and the lake-beds of the eruptions of phonolitic magmas containing shown upon the map. They are all small and of Gold Hill is a mass of augitic syenite-porphyry, High Park, a few miles west of Grouse Mountain, these elements were not followed by intervals of short, and are numerous only near Cripple Creek with many small feldspar and augite crystals in that the grits of Straub and Grouse mountains fumarole and solfataric action. The porous zones town and in Brind Mountain. These are proba­ a very coarse-grained feldspathic groundmass. have been referred to that lake-bed formation. in granite adjoining the phonolite dikes, due to bly of Algonkian age, belonging to a series of Little of the lime-soda or plagioclase feldspar Their thickness in Straub Mountain is 200 feet or removal of quartz and mica, testify to the action wide distribution in the Front Range, and not series is present. Nepheline, sodalite, and nosean more, though the unevenness of the granite floor of agents connected with the phonolite magmas. with the rocks of the volcano. Augite is com· are wanting, but the strongly predominant alkali makes an estimate difficult. Age of the volcano.-An indirect chain of evi­ monly changed to uralitic hornblende in these feldspars ally this rock with the phonolite series. The phonolite mass of Grouse Mountain was dence indicates that the Cripple Creek volcano is dikes. Hornblende and mica are subordinate constituents. laterally intruded into the grits at a time when o£ Miocene age. The late Eocene (Oligocene) Andesite.-The andesites represented upon the Basic dike rocks.-The last eruption of the they must have had a much greater thickness lake-beds of Florissant are overlain by rhyolite map, though not very different in character, are district produced a number of narrow dikes of than at present. The plane of intrusion was seemingly identical with many other remnants, of two principal epochs of eruption. The more dark basic rocks. These are usually very much \-ery irregular, as shown by the map, cutting in including those of High Park and Grouse Moun­ important type is an augite-hornblende-andesite decomposed, but from the few fresh occurrences places down to the granite, and there lifting rhyo· tain. As stated above, the phonolite of the latter with some mica. It is probably the earliest massive it is plain that there are two distinct rock types lite and grit, while in other places one or both of locality is later than the rhyolite, and, by rock of the volcano, and the small areas of Battle among these dikes, one a. nepheline-basalt, the these formations were left between granite and inference, the volcano is, in part at least, younger and Big Bull mountains are regarded as repre­ other a normal feldspar-basalt. The latter type phonolite. The phonolite of Straub Mountain is than the Eocene, though there are no means of senting a large body which has been in great is shown in fresh condition in the Wilson mine likewise an intrusion into the grits.· estimating the duration of the volcanic activity. degree destroyed by explosive outbursts or at Altman, and near the Dolly Varden mine in DESCRIPTION OF THE VOLCANIC CENTER. WHITMAN CROSS, covered by the tuff and breccia of the eruption. Squaw Gulch. The former occurs in numerous . This andesite is characterized by its large pris· dikes in Battle Mountain and Raven Hill, being Relation of tuff-breccia to granite.-The tuffs July, 1895. Geologist. MINING GEOLOGY. veins intersect all rocks in their course, and have their courses or, more commonly, for short dis­ superficially. The water available for use in the been formed mostly by a replacement along the tances, and that when a vein meets a dike, though wet processes is limited in amount, and therefore Generalstatement.-Gold was discovered in the fissures, and not, except to a very small extent, by it may cross it directly, it is likely to be deflected no attempt at "hydraulic mining" has been made. Cripple Creek region about twenty years before the filling of open gaps. and to follow the dike for a greater or less dis­ the recent developments. Two previous periods tance. This association of veins and dikes is one SOURCE OF THE ORE. THE FISSURES. of mining excitement and exploration have . of the prominent features of certain parts of the General statement.-The gold and associated occurred, one in 1874 and one in 1885; but, General features.-The existence of numerous district, and is attributable mostly to the influence vein materials in the district have probably been unlike the recent explorations, they ended with­ dikes in the region indicates the presence of pre­ of the dikes on the vein fissures and in a less derived from the volcanic rocks and, to a less out important results, for no paying mines were existing fissures, so that fissuring action undoubt­ degree to their influence on ore deposition. Ore extent, from the immediately adjacent granite; discovered. edly began sometime before the formation of deposition was a sequel of the dike action, for and they have probably 'not come exclusively The first really valuable discoveries were made dikes; in fact, it is natural to suppose that such it depended largely on the presence of heated from shallow sources nor exClusively from the in 1891. People flocked into the region and the action occurred during the whole of the eruptive rocks, and would be more likely to occur in the immediately adjacent rocks, but from the whole district developed with remarkable rapidity. In epoch of the district. In some places the veins region pf the latest eruptive rocks, which were area of rock in which the underground drainage the fall of 1894 the town of Cripple Creek, which occupy these early fissures, but in a general way the dikes, than elsewhere. The dikes may also was tributary to the fissures at the time of ore came into existence in 1891, had a population of the vein fissures do not seem to have been the have cut water channels existing m the country deposition. The sources of the gold and certain about 10,000, and this, added to the population earliest ones formed, though many of them were rock, and the water from ·such channels, thus aRsociated materials appear to have been the of the neighboring towns and settlements which produced before the dike action ceased. In most forced up tbe sides of the dikes, might haYe eruptive rocks and, to a less extent, the granite, an had sprung up, made a total of about 15,000. cases which have been examined, however, the caused ore deposition. Moreover, the shrinkage origin assumed more on account of the peculiar Over 100 mines and claims more or less devel- fissures occupied by veins were formed after the cracks formed in the dikes at their contacts with environment of the former during ore deposition . oped were being actively worked, while several intrusion of the dikes, as is shown by the fact the country rock may in some cases have offered than on account of any definite knowledge as to thousand claims had been located and partly that they intersect the latter. favorable places for ore deposition~ These causes the relative amounts of gold in these rocks when prospected. The production of the district from The fissuring action affected both the volcanic have doubtless been in some cases more or less in an unaltered condition. The concentration of 1891 to 1894, inclusive, has been variously esti­ area and the surrounding granite, so that the effective in producing a connection between dikes gold in fissures requires not only a source of gold mated at from $5,543,967 to $7,000,000. whole region is much broken by numerous fis­ and veins; but in most cases where veins follow but also the reagents (generally hot solvent solu­ sures intersecting one another at various angles. dikes the association is clearly due to.the purely tions under pressure) necessary to dissolve THE ORES. the In any single locality one general course is usually mechanical· effect of the dikes in directing the disseminated metal, to carry it into the fissures, General featu?·es.-The ores of the Cripple prominent, though intersecting . fissures of less courses of the later fissures in which many of the and there, by one or more of many methods, to Creek district are almost exclusively gold ores. prominence are always present; and in some veins were deposited. deposit it. It is a noticeable fact throughout the A little silver occurs in most of them, and its places there are two or more systems of parallel Ohanqes in veins and dikes at a deptlt.-It is Cripple Creek district that the richest veins occur quantity is sometimes sufficient to be of import, fissuring. The general course of the fissures often noticeable that near the surface both veins in eruptive rocks or in granite in the vicinity of ance, but usually it is insignificant. No other carrying the veins of the district, like that of the and dikes dip at angles different from those seen the vent or vents from which the eruptives were metals occur in any of the ores in quantities of dikes, varies from northeast to northwest; often at a depth; while sometimes veins that occur in ejected. In such positions, as the result of sub­ commercial value. The ore consists usually of it is nearly due north and south. Some of the one well-defined fissure at a depth fork near the siding eruptive activity, the rocks were subject country rock· more or less impregnated and fissures occasionally strike more nearly east and surface and appear in two or more separate out­ to the action of hot waters impregnated with replaced by quartz and other minerals, among west, but in most of the important veins the crops. Both these phenomena can be attributed various solutions; and these w·aters seem to have ·· which the most abundant are fluorite, opaline more northerly trend is distinctly characteristic. to the fact that the district is comparatively been the reagents that dissolved the gold and silica, kaolin, iron pyrites and other iron minerals, The fissures are usually represented by one young geologically and erosion has notyet com­ caused its concentration in fissures. Hence the manganese oxides, and more rarely small quan­ main fractgre with numerous subordinate parallel pletely obliterated the original character of the veins are rich in and near the areas of the vents tities of galena, cerussite, possibly ~mglesitf', mala­ or approximately parallel fractures, though some­ upper parts of the formations. The fissures and become poorer as distance increases; and chite, acanthite, probably chalcopyrite, tetrahe­ times two or more main fractures occur close occupied by the dikes or veins were confined to hence also the eruptive rocks probably supplied drite, stibnite, sphalerite, calaverite, native gold, together; and frequently there is no one specially the original line of breakage at a depth, on most of the gold, while the immediately adjacent · oxidized tellurium minerals, gypsum, calcite, and well-defined break, but a number of closely par­ account of the superincumbent pressure, while granite may have supplied a certain part. numerous other minerals in still smaller quantities. allel fissures of about equal magnitude, giving nearer the surface this pressure was relieved, The other vein materials accompanying the The stibnite, the sphalerite, and the copper min­ the rock a minutely banded or sheeted structure numerous transverse breaks of a more or Jess gold haye probably come from similar sources, erals, including tetrahedrite, are very rare. and forming a fissured zone. The character of the superficial character were encountered, and the though often in a somewhat different manner. It The ores often consist simply of country rock, fissures is much affected by the nature of the fissures were more easily deflected or divided. is probable that the fluorine in the fluorite common either eruptive materials or granite, containing rocks they intersect, for they are sharper and Such effects are not seen in all parts of the dis· in the district originally came into the fissures in secondary quartz and associated minerals, instead better defined in the hard or brittle rocks than in trict, or even in most parts, for erosion has usually a volatile or soluble form, such as hydrofluoric of, as in many gold districts, and, in fact, as in the softer and more plastic ones. removed all signs of them; but they are especially acid, or, more probably, as some of the hydrofluo­ parts of the Cripple Creek district, consisting of The fissures as fault planes.-The fissures are noticeable where erosion has been least. silicates or as soluble fluorides, and there encoun­ well-defined bodies of these materials. A char­ usually the result of movement probably accom­ Latm· movements in the veins.-After and pos­ tered solutions which carried carbonate of lime acteristic ore of. this district is an intimately panied by a certain amount of faulting, as is sibly during the filling of the fissures with ore, derived from the decay of the eruptive rocks or mixed mass of quartz and fluorite, prominent on proved by the occasional occurrence of fragments more or less movement seems in some places to from other sources. The natural result would be account of its brilliant purple color. of rock in the better-defined fissures and the have occurred along them, for in some of the the formation of fluoride of calcium (fluorite). If The qold.-The gold occurs in the ore as native abundance of grooves or slickensides on their veins the mineral contents are cut by longitudinal the fluorine had been previously in the form of or free gold, as telluride of gold, and possibly as faces. The evidence so far obtained indicates breaks. A similar movement seems to have taken hydrofluosilicic acid the precipitation of fluorite auriferous iron pyrites, the last being the least that the faults in the vein fissures have throws place also along the minor fractures that cross would have been accompanied by a deposition important form. The usually superficial mode of varying from a fraction of an inch to several feet. many of the veins, for the latter are sometimes of silica; and as the two materials would thus be occurrence and the physical condition of the Outside of the immediate Cripple Creek district, cut by indistinct cross cracks. formed at approximately the same time the result native gold indicate that it has been largely however, faults of much greater magnitude occur, Ore deposition in shrinkaqe oraak8.-Sometimes would be the intimately associated mixture of derived from the telluride by oxidation, though sometimes with a displacement of over 1,000 feet, cracks or sheeted zones occur in dikes at their quartz and fluorite known as "purple quartz," some of it may have been derived from auriferous as described by Mr. Cross. contacts with the country rock, and follow all which is distinctly characteristic of the district. iron pyrites or may have been. in the free state It has been suggested by some that faulting the curves in the meanderings of the dikes in a Ore slwots.-In Cripple Creek, as in other gold since it was deposited. Most of the gold at a was the cause of the occurrence of the granitic way that would not be likely to characterize inde­ districts, the gold is not uniformly distributerl depth is in the form of a telluride which has breccia between the granite rim and the central pendent and subsequent fissures. The sheeted throughout the fissures in which the veins occur, been determined by Dr. Hillebrand to be calave­ area of volcanic breccia. This material forms a structure here is probably caused by shrinkage of but is concentrated in certain parts into bodies of rite, though other tellurides may also occur. Iron belt from a few feet to several hundred feet in the dikes along the contact with the country rock; ore of varying shape, size, and continuity, known pyrites is abundant, but rarely, if ever, so far as width, and is seen at many places where the con­ during cooling. The shrinkage cracks are proba, ns ore shoots or ore courses. known, carries any considerable amount of gold. tact zone of the granite and the volcanic breccia bly not so deep-seated nor so far-reiwhing as the The shoots trend variously in the fissures, Superficial altemtions of tlLe ores.-Superficial is visible; but its character and mode of occur­ fissures caused by the later dynamic disturbances, though often a general southerly pitch down and alteration has caused the oxidation, hydration, rence make it evident that it is due to volcanic and therefore, when unaffected by such fissures, along the fissure is the most common. This is and leaching of certain minerals in the ore action and not to faulting, though the material they probably have rarely if ever become the most noticeable where the course of the shoot is deposits, as well as the formation of sulphates, itself is more or less broken by later faults. repository of important ore bodies. guided by certain transverse fissures. Elsewhere phosphates, hydrous silicates, tellurites or tellu­ the shoots dip vertically, and more rarely a little THE VEINS. PLACER DEPOSITS. rates, and other oxidized compounds. to the north. They vary from one foot to several Value of the ores.-The value of the ores at General.featw'es.-What has been said of the Since the time of ore deposition more or less hundred feet in width along the fissureE~, and from present shipped from the mines varies from $20 general mode of occurrence of the fissures holds erosion has occurred in the Cripple Creek district a few inches to several feet in thickness. In some to $400 per· ton, though small shipments some­ true of the veins, which are simply bodies of and the veins have been worn down in the same places they have a well-defined columnar shape, times run up to several thousand dollars per ton. secondary minerals filling the fissures. Some­ manner as the country rock. The gold in their in others their forms are highly irregular; in some The district is at present essentially a shipper of times the veins are single well-defined bodies of eroded parts, by virtue of its greater specific grav­ places they outcrop at the surface, in others their only high-grade ores, but with increased facilities ore and sometimes they are thin parallel seams ity, has been concentrated with the gravels in the apex is many feet below the surface; in some for treatment the large quantities of lower-grade filling the fissured zones. They occur in all the gulches and low places, thus forming the placer places they extend continuously as deep as they ores that occur can be used and the production rocks of the district-breccia, massive eruptives, deposits. The country rock itself may contain have yet been followed, in others theyend at a will be correspondingly increased. and granite. The general character and mode of some gold outside of the veins, and this may have comparatively shallow depth, though in some occurrence of the ore make it evident that the supplied a part of the gold in the placer deposits. cases these shallow shoots may be replaced by MODE OF OCCURRENCE OF THE ORES. 'reins are, largely at least, a replacement of the The placers that have been worked lie mostly others at greater depth. General features of the qold deposits.-The gold country rock along very narrow fissures, which immediately north and west of the town of Crip­ The localization of ore in shoots is due in some of the Cripple Creek district occurs both in vein were hardly more than cracks, though occasionally ple Creek, and occupy hollows in the amphithe­ cases to a restricted circulation of ore-bearing deposits and in placer deposits derived from the the ore appears locally to have filled small open ater of hills surrounding the head waters of ·the solutions, guided by the more permeable places decay and erosion of the veins and country rock. places along them. Every gradation can be seen, stream of Cripple Creek, though in many other along fissures and by transverse fractures, while Though the placers have produced considerable from country rock slightly impregnated with ore places throughout the district smaller deposits in other cases it is due to a variety of minor causes. quantities of gold, the veins are far more import­ along a fissure, to country rock completely occur and have been operated to some extent. ant and supply most of the gold of the district. replaced and converted to a well-defined vein. The placers have been worked in many ways­ R. A. F. PENROSE; Jr., They generally occur in fissures in the country Relation of veins to dikes.-It is notable that by the pan, rocker, sluice, and by various forms Geoloqist. rock, which usually represent slight faulting. The the veins often follow dikes, either throughout of dry washers-but have been opened up only July, 1895.