Page:Popular Science Monthly Volume 14.djvu/357

Rh whose influence is very potent, as its power of absorbing and retaining heat is thousands of times greater than that of air. Hence, as the ocean was so largely preponderant, there was an atmosphere heavily charged with moisture, which in time was favorable to a warm and equable climate. In fact, the want of annual rings in carboniferous plants proves that there was no winter, and, as the same coal-plants grew at the same time in Europe and America, the same climate must have prevailed. The air was also charged with carbonic acid, for there are no fossils (which Prof. Huxley so beautifully says are the labels that an Almighty hand has put upon the specimens in Nature's museum) in this or any other earlier formation of warm-blooded animals.

In all these circumstances, therefore, there exist the most advantageous conditions for the rapid and continuous growth of vegetation, and, judging from the fossils thereof, it must have gone on with a density and luxuriance that wellnigh surpasses conception. Floating vegetables first made their appearance, spreading their branches and leaves on the surface of the water, and filling the basin or lagoon with their débris thus forming a support for the more aërial vegetation, compared with which anything in our day of the same species, in respect to size and quantity, fades into insignificance.

The exuberant growth of the tropics is astonishing to us; but it is as nothing when we contemplate that of the coal era. For example: Equisetum, the horse-tail flag, with us is never more than half an inch in diameter, while in the coal-rocks gigantic reeds of this kind were as much as fourteen inches in diameter. Living club-mosses, even in our tropics, attain no great height, but there they were as thick as a man's body and sixty and seventy feet high. Our ferns are of insignificant size, but in those olden days they raised their feathery foliage to a height of sixty feet and upward. There are others that grew to the same wonderful proportions; and as they fell others sprang up, and thus the "heaping" process continued until Nature caused some subsidence of the ground; the water closed over it all, and the currents deposited mud and sand upon it: if the former, a stratum of slate was the ultimate result; if the latter, a stratum of sandstone. When this subsidence ceased, fresh growths sprang up and a new deposit was formed, to sink and be covered in its turn; and as often as these periods of rest and submergence were repeated, so often did a new coal-bed come into existence, and in this is a simple rational explanation why the coal-measures have more than one seam in them.

If, on the other hand, an elevation took place, the roots of the plants were deprived of their moisture, and they not only ceased growing and the deposit accumulating, but the rains and surface-drainage gradually eroded the latter away, and, as it floated off, it became mixed with any earthy matter which the waters may have had in mechanical suspension; and, when it was finally deposited in some lagoon or over-spread other formations, it ultimately made an inferior coal, or a black