68 THE ICE AGE IN CANADA. 



jecting hills, and following old lines of coast. These are 

 evidently of the nature of modern gravel and shingle 

 banks, and are distinguished from moraines and ice-shove 

 deposits by their water-worn and sorted material. 



On the lower St. Lawrence I have observed marine 

 shells on the terraces up to about 600 feet above the level 

 of the sea, but they will probably be found by diligent 

 search at higher levels. In the arctic region, Captain 

 Fielden (Journal of Geol. Society of London, Vol. XXXIV., 

 1878, p. 566) reports Pleistocene shells, viz., Pecten 

 Islandicus, Astarte borealis, Mya truncata and Saxicava 

 rugosa, at the height of 1,000 feet above the sea. 



With the terraces and elevated banks must be associated 

 the later boulder-drift, which has distributed travelled 

 stones and boulders through and over the Saxicava sand 

 and the moraines of older local glaciers, and has deposited 

 them at high levels on hills and mountains far inland. 

 The assignment of such loose boulders to their precise 

 date is, however, often extremely difficult, a fact which 

 may be well seen from a study of the data accumulated by 

 the boulder committee of the Geological Society of Scot- 

 land, under the presidency of my friend, Mr. David Milne 

 Home. Neglecting altogether for the present boulders 

 not far removed from their native sites, some of the far- 

 travelled boulders at high levels may have been left as 

 residue of the denudation of the more elevated sheets or 

 patches of boulder-clay. Others may belong to the 

 driftage of the margins and banks of the mid-glacial 

 depression of the Leda clay, but these can scarcely have 

 reached higher levels than about 600 feet. Others still 

 may have been carried by ice in that short-lived depression 

 of very great magnitude which seems to have immediately 



