No, 3.] DAWSON— POST-PLIOCENE. 251 



surfaces, probably polished by ice, though no striation remains, 

 and largo Laurentian boulders, which must have been carried 

 probably a hundred miles from the Laurentian regions to the 

 north-east, and over the dsep intervening valley of the St. Law- 

 rence. 



I have already, in the first part of this memoir, noticed the 

 striation on rock surfaces at Montreal, and may merely add that 

 it is often very perfect, and must have been produced by a force 

 acting up the St. Lawrence valley from the north-east, and plan- 

 ing all the spurs of the Mountain on that side, while leaving the 

 3Iountain itself as a bare and rugged unglaciated escarpment, [n 

 the streets of Montreal the true Boulder-clay is often exposed in 

 excavations, and is seen to contain great numbers of glaciated 

 stones, most of which are of the hardened Lower Silurian shales 

 and limestones of the base of the Mountain ; and thouQ;h no 

 marine shells have been found, the sub -aquatic origin of the mass 

 is evidenced by its gray unoxidised character, and by the fact 

 that many of the striated stones at once fall to pieces when ex- 

 posed to the frost, so that they cannot possibly have been glaciated 

 by a sub-aerial glacier. 



At the Glen brick-work, near Montreal, the Leda clay and 

 underlying deposits have been excavated to a considerable depth, 

 and present certain remarkable modifications. The section ob- 

 served at this place is as follows : 



ft. in. 



1. Hard gray laminated clay, Foraminifera and Leda, in thin 



layers 7 



2. Red layer, in two bands 6 



3. Sandy clay 1 o 



4. Gray and reddish clay 9 o 



5. Hard buff sand, very fine and laminated 15 



6. Sand with layers of tough clay, holding glaciated stones, 



and very irregularly disposed 4 



7. Fine sand 1 



8. Gray sand, with rounded pebbles, and laminated ob- 



scurely and diagonally 4 



9. Fine laminated yellow sand 3 



10. Gravel 4 



11. Very irregular mass of laminated sand, with mud, gravel, 



stones and large boulders 12 



56 10 



