Page:Popular Science Monthly Volume 13.djvu/667

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GEOLOGICAL HISTORY OF NEW YORK.

but none such have yet been discovered, while a number of well-known European Triassic species have been obtained from what are considered as the highest portions of the group in Virginia and North Carolina.

In the Cretaceous age the region about New York sunk below its Triassic level, and the sea came in over a belt of country which was before, and is now, dry land. The waves in their advance cut away much of the shore which opposed their progress, both rock and soil, and spread a sheet of sea-beach composed of gravel and sand as far as they reached inland. This old beach we now know as the Raritan sands, and they contain great quantities of leaves, branches, and trunks of trees, which had grown on the sinking coast. On examination, they prove to be entirely different from those contained in the Triassic rocks, consisting mainly of the remains of angiospermous plants—the highest botanical group, and such as form the prevailing vegetation of the present day. Among these Cretaceous plants we find the leaves of oaks, magnolias, and other genera now living in our forests. These prove that, in the long interval—the Jurassic age—which intervened between the Triassic and Cretaceous, the vegetation of the world had been completely revolutionized; at least, that most of the genera and species which prevailed during the Triassic age had passed away, and been superseded by such as had been before unknown.

When the water stood at a moderate depth over the sunken shore, the Amboy clays settled down upon the sandy bottom. These were apparently derived from the feldspar of the granites which compose the neighboring highlands; the quartz, unaffected by chemical action, and less finely comminuted, remaining as sand and gravel nearer its place of origin.

As the water deepened, true marine conditions supervened along the coast, and the first two of the New Jersey marl-beds were formed from the remains of animals which inhabited the sea, and such as were washed into it from the adjacent shore. The green-sand of these marl-beds is derived chiefly from the countless number of microscopic shells of the Foraminifera, which filled the waters of the Cretaceous sea here, as in many other places. Its green color is due to glauconite, a silicate of lime, potash, alumina, etc. White chalk is likewise composed chiefly of the shells of Foraminifera, but these lived in deeper water, and were of different kinds from those that produced the greensand. The fertilizing property of the marls is due to the potash and phosphorus they contain.

The marl-beds are also vast cemeteries, in which are stored the more or less perfect remains of the larger land and water animals of Cretaceous times. Among these we find the shells of Ammonites—the great coiled cephalopods—and a large number of other mollusks characteristic of the Cretaceous fauna. There have likewise been discovered in the marl-beds numerous remains of large reptiles, both herbivorous and carnivorous. Among these are Hadrosaurus and Lœlaps—the represent-