644 THE POPULAR SCIENCE MONTHLY. 



The trough between the New York axis and the Blue Ridge was occu- 

 pied by water, and in this trough the Triassic shales and sandstones 

 were deposited. A similar trough east of New York, where now is the 

 valley of the Connecticut, was also a lagoon or estuary in which similar 

 sediments accumulated, but not so quietly as the strata composing the 

 older formations in the same region were laid down. It is evident that 

 Nature's forces were in great activity during the period under consider- 

 ation, for we find the greatest diversity in the product of these forces. 

 The Triassic beds consist of shales, sandstones, and conglomerates. Of 

 these the shales accumulated in comparatively clear and quiet water; 

 and at various levels we find them filled with the remains of fishes that 

 inhabited the lagoons where they were deposited. These fishes occur 

 in thousands, confined to layers a few inches thick, mostly complete 

 and mature individuals, showing that they were killed suddenly by some 

 poisoning of the water in which they lived, its complete withdrawal, or 

 a substitution of fresh for salt, or vice versa. These fish-bearing shales 

 alternate with conglomerates that are sometimes beds of large bowl- 

 ders the result of violent water-action alone: a shore or with strata 

 of ripple-marked, sun-cracked sandstone, pitted with the impressions of 

 rain-drops, and bearing the footprints of thousands of animals, great 

 and small, which made these mud-banks their feeding-grounds. Here 

 and there we find twigs of coniferous trees of the Araucarian family, or 

 fragments of the fronds of cycads and ferns ; much more frequently casts 

 of the trunks and branches of trees mingled pell-mell, and evidently col- 

 lections of drift-wood. 



The footprints referred to above are generally three-toed, and resem- 

 ble the tracks of birds. In dimension they vary from one to twenty 

 inches long, and are supposed to have been made by a peculiar group of 

 biped, birdlike reptiles, which possessed the world in Mesozoic times, 

 and inhabited the shores of North America in great numbers during the 

 Triassic age. 



The alternations of coarse and fine strata, with their characteristic 

 fishes and footprints, are repeated in the Trias on the west side of the 

 Hudson until they form a series which has a thickness of several thou- 

 sand feet. As the ripple-marks, sun-cracks, and other evidences of 

 exposure to the air, occur at several levels, they prove the gradual sub- 

 sidence of the trough where those sediments accumulated, with which 

 the filling from the wash of the land kept pace, affording a succession 

 of fresh surfaces where the winds and waves as well as living creatures 

 left their autographs. Although as yet but partially examined and 

 imperfectly read, these records, like the Assyrian tablets, have told us 

 many interesting things, and they constitute a treasury of ancient lore 

 which is destined for ages to supply new material for the geological 

 historv of this region. 



From what we have already learned of the circumstances in which 

 the Triassic rocks of our neighborhood were formed, we may conclude 



