Reviews — Sir J. W. Dawson — Canadian Ice-Age. 275 



and the Belly Eiver in the North-west Territory. Beneath the 

 Lower Boulder-clay the Palgeozoic rocks are glaciated; and striae 

 and boulders alike indicate movement from north-east to south-west, 

 from the Atlantic up the valley of the St. Lawrence. The Boulder- 

 clay, which by damming the more ancient valleys, forms the basins 

 of the great Canadian lakes, is of similar character to the material 

 of the Missouri coteau or prairie escarpment of the west, which is 

 regarded as the deposit at the margin of a sea laden with floating 

 ice. The Lower Leda-clay is like the deposits now forming beneath 

 the ice in Baffin's Bay and the Spitzbergen Sea. But the Upper 

 Leda-clay appears to indicate more temperate conditions, since nearly 

 all its fossils have been dredged in the Gulf of St. Lawrence ; and 

 the land plants which it yields still live on the north shore of the 

 St. Lawrence. Some of the Leda-clays occur 600 feet above sea- 

 level, while the beds include littoral gravels and sand, so that 

 considerable changes of level are associated with their deposition. 

 Subsequently extensive local glaciers clothed the Appalachian chain 

 in the east, and the Cordilleran region of the west, where the 

 deposits have been especially investigated by Dr. G. M. Dawson, 

 and are regarded as indicating as great an elevation of land during 

 the Upper Boulder-clay as was attained during the Lower Boulder- 

 clay. Only when the Cordilleran region was at its maximum 

 elevation the region of the great plains experienced a correlative 

 subsidence and submergence ; while the intervening subsidence 

 between the two glaciations of the Cordilleran region is associated 

 with the elevation of the plains, which led to the formation of great 

 lakes in which inter-Glacial deposits and peat were formed. The 

 second elevation of the west was followed by a partial subsidence 

 to a level of about 2500 feet, with a long stage of stability during 

 which white muds were deposited, and when the renewed elevation 

 took place the shore-line stood about 200 feet lower than at present. 



The Lower Boulder-clay over a great part of Canada is thickly 

 packed with boulders ; though in Triassic and Upper Carboniferous 

 areas it becomes an incoherent sand. The stones are often scratched 

 and grooved. They are mostly from the neighbouring rock- 

 formations. In the lower valley of the St. Lawrence they are 

 chiefly Laurentian gneiss from the north-east. The clay fills up 

 valleys and depressions, and is thin or absent on the high ground. 

 The striations beneath the Boulder-clay in New England run to 

 the south-east, but there is also a south-west direction, a south 

 direction, and occasionally the striee are east and west. The north- 

 east to south-west direction is attributed to the Arctic current, 

 especially when associated with marine organisms. But where the 

 striaa are upon mountains they are attributed to land-ice. Thus, on 

 the south of the St. Lawrence, the Notre Dame Mountains show 

 strige which descend south towards the Baie des Chaleurs, and north 

 towards the St. Lawrence. The phenomena indicate oscillations 

 in level of the land. 



The excavation of the basins of the great American lakes in the 

 softer members of Silurian and Devonian formations is said to be 



