398 GEOLOGY. 



it appear more impoverished than it really was. The shore tracts 

 were then far out on the borders qf the continental platform, and the 

 deposits there made were buried beneath later deposits when the sea 

 readvanced, and have been specially subject to further burial by sub- 

 sequent border deposits. Large portions of these tracts are probably 

 now under the sea. They are, therefore, of all epicontinental deposits 

 least accessible to observation. 



Aside from the lessened area, the life conditions were probably 

 less favorable, area for area, than in the stage of sea expansion, for 

 the wash from the land was presumably augmented by the increased 

 land area and the greater relief of the land caused by the lowering 

 of the sea-level, if not also, as is probable, by the upward bowing of 

 the continental surface. The increased detritus poured by the rivers 

 into the coast belt probably inhibited some forms of life, injured others, 

 and helped but a few. Some of the basins or embayments were doubt- 

 less affected by too great freshness of water and some by too great 

 salinity, and what was probably more unfavorable for life, by alter- 

 nations from the one to the other. 



These general characterizations find exemplification in the meager- 

 ness of the faunas of the Shawangunk grit, the Oneida conglomerate, 

 and the Medina sandstone, all of which are very barren of fossils. Grant- 

 ing that some part of this barrenness may be due to the dissolving 

 away of relics once contained in the beds, there can be little doubt 

 of an original barrenness, for whatever may be true of the coarse sand- 

 stones, there is no reason to assume exceptional solution of organic 

 substances in the abundant shales and fine-grained argillaceous sand- 

 stones. 



In the earliest beds referred to the Medina in the eastern interior, 

 there are a few lingering Ordovician species. Then follows the great 

 mass of the Medina formation in which practically no determinable 

 life relics appear, while near the top of the deposit a meager fauna of 

 the post -transition type initiates the distinctive Silurian fauna. 

 Scarcely more than a dozen species of invertebrates have been identi- 

 fied, and these have a pauperitic aspect that seems to tell of the hard 

 conditions under which they lived. The very fact that the Medina 

 shales and sandstones are prevailingly red, probably tells a tale of 

 hostility to life, but we cannot read it with much assurance at present. 



