THE SUCCESSION OF DEPOSITS. 39 



glaciated liunps of Utica shale and other soft rocks, which 

 become disintegrated at once when exposed to weathering. 



The true boulder-clay is in all ordinary cases the oldest 

 member of the Pleistocene deposits, and it is not possible 

 to divide it into distinct boulder-clays of different 

 ages, superimposed on one another. It may be observed, 

 however, that in so far as the boulder-clay is a marine 

 deposit, that which occurs at lower levels is in all pro- 

 bability newer than that which occurs at higher levels. 

 It is also to be observed that boulders with layers of 

 stones occasionally occur in the Leda clay ; and that the 

 superficial sands and gravels sometimes contain large 

 boulders, and even constitute an upper or new^er boulder 

 formation ; but these appearances are not usually sufh- 

 ciently important to cause any experienced observer to 

 mistake such overlying deposits for the lower boulder-clay. 

 They belong to the second or newer part of the period. 



In some localities the stones in the boulder-clay are 

 almost exclusively those of the neighbouring rock forma- 

 tions, and this is especially the case at the base of cliffs or 

 prominent outcrops, whence a large quantity of material 

 would be easily derived. In other cases, though less 

 frequently, material travelled from a distance largely 

 predominates. Throughout the valley of the Lower St. 

 Lawrence, the gneiss and other hard metamorphic rocks 

 of the Laurentian hills to the north-east are very 

 abundant, and in boulders of large size and much rounded. 

 Occasional instances also occur where large boulders have 

 been transported to the northwards ; but these are com- 

 paratively rare, except in the second or upper drift. I 

 have mentioned some examples of this in "Acadian 

 Geology," p. 61. Similar instances are mentioned in the 

 " Geology of Canada/' p. 893. 



