990 HISTORICAL GEOLOGY. 



rivers, which under the high slopes of the Glacial period had produced pro- 

 found channels, into quiet streams that made fluvial deposits along the way, 

 and often, when in gentlest flow, still-water deposits. It has been shown 

 that when Champlain time began, the ice had already retreated to the moun- 

 tains, and, with this exception, had left New England and the states to the 

 westward. Enough ice still remained, however, to give waters freely, and 

 some floating ice also, to the streams which had their sources near the 

 borders. 



The absence of the ice sheet from the St. Lawrence valley after the mak- 

 ing of the lower fourth of the deposits, is proved by the presence in the beds 

 of shells of Mollusks and relics of other species that lived in the waters when 

 the 100-foot level, near Montreal, was in progress ; and also in Lake Cham- 

 plain, when but 50 feet of the beds had been laid down. Seals and Whales 

 would not have gone beneath the ice hundreds of miles for a Champlain 

 resort. Moreover, since the St. Lawrence River makes four degrees of north- 

 ing on its way to the sea, the evidence proves that the clearing from ice 

 extended as far north as the borders of Labrador. 



But it is important to remember that the river valleys were to some extent 

 the courses of streams in the Glacial period, and therefore that beds of the 

 Champlain period may rest on others of clay or sand which are Glacial in 

 period of formation. Sometimes these fluvial beds of the Glacial period may 

 be distinguished by the presence of bowlders ; but this criterion is not alto- 

 gether safe, since floating ice of the Champlain period may have been the 

 source of the bowlders. At the North Haven clay-pits, a few miles north of 

 New Haven, the straticulate clays contain a few bowlders two or three feet 

 in diameter ; and it was in one of these clay-pits that the two bones of Arctic 

 E-eindeer were found, mentioned on page 946. The time of deposition was 

 probably in the earliest part of the Champlain period or the later of the 

 Glacial. 



Deposits of clay appear to have been most abundant in the early part of 

 the Champlain period, after the subsidence had reached its extreme limit, 

 when the flow of the streams having a southward course was feeble. The 

 later increase in the waters, raising the flood level, involved an increase in 

 the pitch of the surface, and therefore a quicker flow ; and then sands suc- 

 ceeded to the clays, and in many regions still coarser deposits, ending often 

 with the coarsest cobblestone deposits when the flood was at its height. 



The stratification of the deposits hence varies from the most regular, or 

 that of gently-moving waters, to that which could form only under a vast 

 shmdtaneous supjjly of gravel or sand, and ivater. The floiv-and-phmge style 

 of deposition (page 93) is common. Beds of this kind occur with others 

 of horizontal bedding, or sometimes locally in the midst of coarse gravel 

 deposits, such stony gravel not participating in it because of its coarseness. 

 Very often, also, the beds indicate that after deposition large portions had 

 been washed away by some local rush of the flooded stream, and that later 

 the excavations thus made became filled. 



