Geology and Mineralogy considered with reference to Natural Theology/Chapter 7
CHAPTER VII.
Strata of the Transition Series.
Thus far we have been occupied with rocks, in which we trace chiefly the results of chemical and mechanical forces; but, as soon as we enter on the examination of strata of the Transition Series, the history of organic life becomes associated with that of mineral phenomena.[1]
The mineral character of the transition formations presents alternations of slate and shale, with slaty sandstone, limestone, and conglomerate rocks; the latter bearing evidence of the action of water in violent motion; the former showing, by their composition and structure, and by the organic remains which they frequently contain, that they were for the most part deposited in the form of mud and sand, at the bottom of the sea.
Here, therefore, we enter on a new and no less curious
than important field of inquiry, and commence our examination
of the relics of a former world, with a view to ascertain
how far the fossil members of the animal and vegetable
kingdoms may, or may not, be related to existing genera
and species, as parts of one great system of creation, all
bearing marks of derivation from a common author.[2]
Beginning with the animal kingdom, we find the four great existing divisions of Vertebrata, Mollusca, Articulata, and Radiata, to have been coeval with the commencement of organic life upon our globe.[3]
No higher condition of Vertebrata has been yet discovered in the transition formation than that of fishes, whose history will be reserved for a subsequent chapter.
The Mollusca,[4] in the transition series, afford examples of several families; and many genera, which seem at that time to have been universally diffused over all parts of the world; Some of these, (e. g, the Orthoceratite; Spirifer, and Producta) became extinct at an early period in the history of stratification, whilst other genera (as the Nautilus and Terebratula) have continued through all formations unto the present hour.
The earliest examples of Articulated animals are those afforded by the extinct family of Trilobites, (see Plates 45 and 46) to the history of which we shall devote peculiar consideration under the head of Organic Remains. Although nearly fifty species of these Trilobites occur in strata of the transition period, they appear to have become extinct before the commencement of the secondary series.
The Radiated Animals are among the most frequent organic remains in the transition strata; they present numerous forms of great beauty, from which I shall select the family of Crinoidea, or lily-shaped animals allied to Star-fish, for peculiar consideration in a future chapter. (See Pl. 47, Figs. 5, 6, 7.) Fossil, corallines also abound among the radiata of this period, and show that this family had entered thus early upon the important geological functions of adding their calcareous habitations to the solid materials of the strata of the globe. Their history will also be considered in another chapter.
Remains of Vegetables in the Transition Series.
Some idea may be formed of the vegetation which prevailed
during the deposition of the upper strata of the transition
series, from the figures represented in our first plate
(Fig. 1 to 13.) In the interior regions of this series plants
are few in number, and principally marine;[5] but in its
superior regions the remains of land plants are accumulated
in prodigious quantities, and preserved in a state
which gives them a high and two-fold importance; first, as
illustrating the history of the earliest vegetation that appeared
upon our planet, and the state of climate and geological
changes which then prevailed;[6] secondly, as affecting, in
no small degree, the actual condition of the human race.
The strata in which these vegetable remains have been
collected together in such vast abundance have been justly
designated by the name of the carboniferous order, or great
coal formation. (See Conybeare and Phillips's Geology of
England and Wales, book iii.) It is in this formation
chiefly, that the remains of plants of a former world have
been preserved and converted into beds of mineral coal;
having been transported to the bottom of former seas and
estuaries, or lakes, and buried in beds of sand and mud,
which have since been changed into sandstone and shale.
(See Pl. 1, sec. 14.)[7]
Besides this coal, many strata of the carboniferous order 5 contain subordinate beds of. a rich argillaceous iron ore, which the near position of the coal render easy of reduction to a metallic state; and this reduction is further facilitated by the proximity of limestone, which is requisite as a flux to separate the metal from the ore, and usually abounds in the lower regions of the carboniferous strata.
A formation that isat once the vehicle of two such valuable mineral productions as coal and iron, assumes a place of the first importance among the sources of benefit to mankind; and this benefit is the direct result of physical changes which affected the earth at those remote periods of time, when the first forms of vegetable life appeared upon its surface.
The important uses of coal and iron in administering to the supply of our daily wants, give to every individual amongst us, in almost every moment of our lives, a personal concern, of which but few are conscious, in the geological events of these very distant eras. We are all brought into immediate connexion with the vegetation that clothed the ancient earth, before one-half of its actual surface had yet been formed. The trees of the primeval forests have not, like modern trees, undergone decay, yielding back their elements to the soil and atmosphere by which they had been nourished; but, treasured up in subterranean storehouses, have been transformed into enduring beds of coal, which in these latter ages have become to man the sources of heat, and light, and wealth. My fire now burns with fuel, and my lamp is shining with the light of gas, derived from coal that has been buried for countless ages in the deep and dark recesses of the earth. We prepare our food, and maintain our forges and furnaces, and the power of our steam-engines, with the remains of plants of ancient forms and extinct species, which were swept from the earth ere the formation of the transition strata was completed Our instruments of cutlery, the tools of our mechanics, and the countless machines which we construct, by the infinitely varied applications of iron, are derived from ore, for the most part coeval with, or more ancient than the fuel, by the aid of which we reduce it to its metallic state, and apply it to innumerable uses in the economy of human life. Thus, from the wreck of forests that waved upon the surface of the primeval lands, and from ferruginous mud that was lodged at the bottom of the primeval waters, we derive our chief supplies of coal and iron; those two fundamental elements of art and industry, which contribute more than any other mineral production of the earth, tot increase the riches, and multiply the comforts, and ameliorate the condition of mankind.
- ↑ It is most convenient to include within the Transition series, all kinds of stratified rocks, from the earliest slates, in which we find the first traces of animal or vegetable remains, to the termination of the great coal formation. The animal remains in the more ancient portion of this series, viz. the Grauwacke group, though nearly allied in genera, usually differ in species from those in its more recent portion, viz. the Carboniferous group.
- ↑ In Plate 1, I have attempted to convey some idea of the organic re mains preserved in the several series of formations, by introducing over each, restored figures of a few of the most characteristic animals and vegetables that occupied the lands and waters, at the periods in which they were deposited.
- ↑ "It has not been found necessary, in discussing the history of fossil plants and animals, to constitute a single new class; they all fall naturally into the same great sections asfthe existing forms.—We are warranted in concluding that the older organic creations were formed upon the same general plan as st present. They cannot, therefore, be correctly described as entirely different systems of nature, but should rather be viewed as corresponding systems, composed of different details. The difference of these details arises mostly from minute specific distinctions; but sometimes, especially among terrestrial plants, certain crustaea, and reptiles, the differences are of a more general nature, and it is not possible to refer the fossil tribes to any known recent genus, or even family. Thus we find the problem of the resemblance of recent and fossil organic beings to resolve itself into a general analogy of system, frequent agreement in important points, but almost universal distinction of minute organization."—Phillips's Guide to Geology, p. 61-63, 1834.
- ↑ In this great division, Cuvier includes a vast number of animals having soft bodies, without any articulated skeleton or spinal marrow, such as the Cuttle-fish, and the inhabitants of univalve and bivalve shells.
- ↑ M. A. Brongniart mentions the occurrence of four species of fucoids in the transition strata of Sweden and Quebec; and Dr. Harlan has described another species found in the Alleghany Mountains.
- ↑ The nature of these vegetables, and their relations to existing species, will be considered in a future chapter.
- ↑ The most characteristic type that exists in this country of the general condition and circumstances of the strata composing the great carhoniferous order, is found in the north of England. It appears from Mr. Forster's section of the strata from Newcastle-upon-Tyne to Cross Fell, in Cumberland, that their united thickness along this line exceeds 4,000 feet. This enormous mass is composed of alternating beds of shale or indurated clay, sandstone, limestone, and coal: the coal is most abundant in the upper part of the series, near Newcastle and Durham, and the limestone predominates towards the lower part; the individual strata enumerated by Forster, are thirty-two beds of coal, sixty-two of sandstone, seventeen of limestone, one intruding bed of trap, and one hundred and twenty-eight beds of shale and clay. The animal remains hitherto noticed in the limestone beds are almost exclusively marine; hence we infer that these strata were deposited at the bottom of the sea. The fresh-water shells that occur occasionally in the upper regions of this great series show that these more recent portions of the coal formation were deposited in water that was either brackish or entirely fresh. It has lately been shown that fresh water deposites occur also occasionally in the lower regions of the carboniferous series. (See Dr. Hibbert's account of the limestone of Burdie House, near Edinburgh; Transactions of the Royal Society of Edinburgh, vol. xiii.; and Professor Phillips's Notice of fresh-water shells of the genus Unio, in the lower part of the coal series of Yorkshire; London Phil. Mag. Nov. 1832, 349.) The causes which collected these vegetables in beds thus piled above each other, and separated by strata of vast thickness, composed of drilled sand and clay, receive illustration from the manner in which drifted timber from the existing forests of America is now accumulated in the estuaries of the great rivers of that continent, particularly in the estuary of the Mississippi, and on the River Mackenzie. See Lyell's Principles of Geology, 3d edit. Vol. iii. Book iii. Ch. xv. and Prof. Phillips's Article Geology in Encyclopaedia Metropolitana, Pt. 37, page 596.