CHAPTER V. 369. the Formations Numbered and Concisely Tabulated
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150 GEOLOGICAL STRUCTURE AND FORMATIONS. CHAPTER V. ENUMERATION AND SEQUENCE OF FORMATIONS IN TENNESSEE. FORMATIONS NUMBERED AND TABULATED—COMPARATIVE TOPOGRAPHICAL AND STRUCTURAL IMPORTANCE—THE COMPLETE SERIES ESTABLISHED BY GEOLOGISTS—UNABRIDGED TABLE OF TENNESSEE FORMATIONS. 369. The Formations Numbered and Concisely Tabulated.—The rocks of Tennessee are, in this Report, grouped into Thirteen Principal Formations. (§ 318.) Most of these are natural, and may be considered as established; others are provisional, and may be changed. A number of them include minor groups of more or less importance, and to these, also, as as matter of convenience, the name Formation will sometimes be applied. The main groups, commencing with the lowest in the series, are numbered consecutively, from 1 to 13; and their subdivisions are designated by adding letters to these numbers. On this and the next page, is a table giving the names of the formations, and the order in which they occur. It is to be read from the bottom, upward, 1 being the lowest formation and 13 the topmost. ABRIDGED TABLE OF TENNESSEE FORMATIONS. SEQUENCE AND TABLES OF FORMATIONS. 151 370. Comparative Topographical and Structural Importance of the Formations.—It must not be inferred that groups of the same rank in the table, are of equal importance in their relations to the topography and rocky structure of the State. This is far from being the case. Several of them have very little importance of this kind. The Black Shale, for instance, though a wide-spreading formation, and, in other respects, one full of interest, contributes little to the topography, or to the rocky mass of the State. Again, any one, even of the subgroups 2, a, 2, b and 2, c, has more topographical importance than have the groups 5, d, (excluding 5a,) 6 and 7 together. The in- 152 GEOLOGICAL STRUCTURE AND FORMATIONS. terest attached to the formations in making up the surface of the State, or as elements in its structure, is, in a measure, pro- portionate to their respective thicknesses. There are, however, other characters to be considered, as, for instance, hardness and durability. 371. In thickness, as will be seen further on, the leading formations differ much. While the Potsdam (2) is many thousand feet thick, most of the others are not as many hundred, and some of them do not reach one hundred. It is to be remarked, however, that several of those, which, in Tennessee, are thin, increase in thickness when traced into other States. 372. The Thinning out of Formations in Tennessee.—The formations occurring in the States of New York and Pennsyl- vania, present quite a complete series, which is often referred to as a standard, by American geologists. Several of the numbers of this series, though very thick in the States mentioned, grow thinner when traced southward, and finally, thin out, and disappear before reaching Tennessee. Others, extending further south or southwest, have their feather edges in Tennessee; as, for instance, the Lower Helderberg, and, to a certain extent, the Black Shale, as well as the sub-group of the Niagara—the Clinch Mountain Sandstone. The Tennessee series is, therefore, less complete than the northern. Not only are some of the formations wholly absent, but others are reduced to very thin beds. 373. But further: certain Alabama and Mississippi formations run out in Tennessee, as well as some of the northern ones. This is true of the sub-groups of the Cretaceous, which, in the States mentioned, are very heavy, but in Tennessee, thin out and disappear. This absence and thinning out of formations, is one of the geological peculiarities of Tennessee. 374. The Complete Series of Formations as established by Ge- ologists.—In order to be able to compare the Tennessee series with the general one made out by geologists, I give the latter as found in Dr. Dana's most excellent Text-Book, and what the author says in explanation. But first, the reader must bear in mind that the strata were formed in succession, and that each stratum, more or less loaded SEQUENCE AND TABLES OF FORMATIONS. 153 with organic remains, is part of a record of the changes, both phy- sical and organic, that were going on during a certain portion of past time. (§§ 327 to 329, inclusive.) The strata are thus the leaves of a great book, in which may be read the history of changes in the oceans and lands, in the atmosphere and climate, in plants and animals; the history, in a word, of the earth's physical and organic progress. The formations may be regarded as chapters in the history, each containing the record of a period, or part of a period. By careful study of the whole series of formations, especially with reference to organic remains, it is found that the history is divided into several distinct parts, (groups of formations,) each the record of a great age, embracing several periods. Corresponding to these parts, we have as many ages. In Dana's own words, the following have been ascertained: * "(1.) There was, first, an age, or division of time, when there was no life on the globe; or, if any existed, this was true only in the latter part of the age, and the life was probably of the very simplest kind. (2.) There was next an age, when Shells, Mollusks, Corals, Crinoids and Trilobites, abounded in the oceans, when the continents were almost all beneath the salt waters, and when there was, as far as has been ascertained, no terrestrial life. (3.) There was next an age, when, besides Shells, Corals, Crinoids, Trilobites and Worms, there were Fishes in the waters, and when the lands, though yet small, began to be covered with vegetation. (4.) There was next an age, when the continents were at many successive times largely dry or marshy land, and the land was densely overgrown with trees, shrubs and smaller plants, of the remains of which plants, the great coal- beds were made. In animal life, there were, besides the kinds already mentioned, various Amphibians and some other Reptiles of inferior tribes. (5.) There was next an age, when Reptiles were exceedingly abundant, far outnumbering and exceeding in variety, and many, also, in size, and even in rank, those of the present day. (6.) There was next an age, when the Reptiles had dwindled, and Mammals or Quadrupeds were in great numbers over the continents; and the size of these Quadrupeds, like that of the Reptiles in the preceding age, was far greater than the size of modern species. (7.) After this came Man, and the progress of life here ended. The above-mentioned ages in the progress of life and the earth's history, have received the following names: *Text-book of Geology, pp. 63-66. 154 GEOLOGICAL STRUCTURE AND FORMATIONS. SEQUENCE AND TABLES OF FORMATIONS. 155 NOTE.-This section is the same as that in the Text-book, with the exception of the right hand column, which has been introduced in order to show the Tennessee Divisions. 1. AZOIC TIME OR AGE.—The name is from the Greek a, not or without, and zoe, life. 2. AGE OF MOLLUSKS, or the SILURIAN AGE. 3. AGE OF FISHES, or the DEVONIAN AGE. 4. AGE OF COAL-PLANTS, or the CARBONIFEROUS AGE. 5. AGE OF REPTILES, or the REPTILIAN AGE. 6. AGE OF MAMMALS, or the MAMMALIAN AGE. 7. AGE OF MAN. The first of these ages—the Azoic—stands apart as the preparatory time for the commencement of the systems of life. The next three ages were alike in many respects, especially in the air of antiquity pervading the tribes that then lived, the shells, crinoids, corals, fishes, coal-plants, and 156 GEOLOGICAL STRUCTURE AND FORMATIONS. reptiles belonging to tribes that are now wholly or nearly extinct. The era of these ages has, therefore, been appropriately called Paleozoic time, the word Paleozoic, coming from the Greek palaios, ancient, and zoe, life. The next age was ushered in after the extinction of many of the Paleozoic tribes, and its own peculiar life approximated more to that of the existing world. Yet it was still made up wholly of extinct species, and the most prominent of the tribes and genera disappeared before, or at its close. This age corresponds to Medieval time in geological history, and is called Mesozoic time, from the Greek mesos, middle, and zoe, life. The next age was decidedly modern in the aspect of its species, the higher as well as lower, although only a few of those of its later epochs survive into the age of Man. It is called Cenozoic time, from the Greek kainos, recent, and zoe, life, (the ai of the Greek words always becoming e in English, as, for example, in ether, from the Greek aither.) The following are, then, the grand divisions of geological time, adopted: I. AZOIC TIME. II. PALEOZOIC TIME, including (1) The Age of Mollusks, or Silurian; (2) The Age of Fishes, or Devonian; (3) The Age of Coal-plants, or Carboniferous. III. MESOZOIC TIME, including the Reptilian Age. IV. CENOZOIC TIME, including the Mammalian Age. V. The AGE OF MIND, or the Human Era. The foregoing section represents the successive formations of the globe, arranged in the order of time, with the subdivisions corresponding to the Ages and Periods. The various strata in the formations of an age, are very diversified in char- acter, limestones being overlaid abruptly by sandstones, conglomerates or shales, or either of these last, by limestones; and each may be very different from the following in its fossils. These abrupt transitions in the strata are proofs that there were great changes, at times, in the conditions of the region where the strata were formed; and the transitions in the kinds of fossils are evidence of great destruction, at intervals, in the life of the seas.