TERTIARY SYSTEM. 169 
like. Reptiles are also found similar to those in the Wealden. Bones of 
birds have been discovered, as also bones of what seems to be a species of 
monkey. 
Scenery.—The Chalk series appears to be wholly a marine deposit. The 
Jand we know little or nothing of; suflicient, however, to shew that it was 
clothed with vegetable life, as in other periods, but little to picture its 
appearance. “Over it, huge Wealden reptiles sought their prey, birds flew, 
and great apes swung from tree to tree. But the ocean swarmed with 
varied life, mild sea-breezes blew, and smiling sunbeams sparkled 
upon its waters ; for the climate was warm, as shewn by the corals, rep- 
tiles, and monkeys. In the tepid waters lived numberless fishes and 
shells, and on their surface the nautilus spread its coloured sail. — 
The origin of chalk is a problem not yet satisfactorily settled, but the 
generally received opinion is, that the shores weretffringed by coral 
reefs, which the dashing waves gradually wore down into fine powder, as 
they still do in tropical seas, while millions of shell-fish teemed in. its 
waters, and left their white shells as an impalpable sand, that, under the 
microscope, shews the tiny houses of the old inhabitants as perfect as on 
the day they died. Flint seems mostly to consist of concretions round 
sponges, corals, and other substances, and may be found at any epoch, and 
occurs in many other formations besides the Chalk, though there in 
greatest abundance. ' 
XI.—Tertiary System. 
We have now arrived at a new epoch in the history of the rocks, 
known as the Epoch of Recent Life. Henceforward, the plants and 
animals bear not only a close resemblance to those now existing, but a 
great proportion of them are identical. We discover real ext emous trees, 
the same corals, crustaceans, and shells, equal-lobed fishes, birds, and 
mammals of existing families—and all these not only more numerous than 
hitherto, but also more perfectly preserved. The name given to this 
system is a relic of the names used in early geology, when all rocks were 
divided into Primary, Secondary, and Tertiary. In the Tertiary System, 
two great periods are easily distinguishable: 1. The Warm Period; 2. The 
Cold Perwod. 
1. Toe Warm TERTIARY PERIOD.—This system exhibits clays, sands loose 
or hard, gypsum or plaster of Paris, and marls. The only true rock is 
limestone, made up of innumerable little shells, so numerous that the 
stone, which is extensively found throughout the world, is named from its 
coin-like shells, nummulitic.1 The limestone is burned for various pur- 
poses ; the clays are extensively used ; the harder sands are employed for 
PE obey . 
1 From Latin nummus, a @oin. 
