1<)0 THE ICK A(;K in CANADA. 



The (leprc'ssioiis between these ridges are occupied with 

 I'leistoceiie dejtosits, not so re_t;'ular and unifi)rni in 

 their arvunj^fement as the eoi'respon(Hn_tf lieds in the ,L,'reat 

 ])lains higher u]) th(> St. Lawrence, but still presenting a 

 more or less detinite order of succession. The oldest 

 member of the d(']K)sit is a tough boulder-clay, its cement 

 foi'med of gray or rtuldish mud derived from the waste of 

 the shales of the (^)uebe(' grouj), and the stones and 

 boidders with which it is filled ])artly derived from tiie 

 harder meml)ers of that grou]), and jiartly from the 

 Laurontian hills (tn the ()]»])osite or northern side of the 

 rivei', here more than twenty miles distant. The thick- 

 ness of this boulder-clay is, no doul)t, very variable, but 

 does not a})pear to be so great as farther to the eastward. 



Above the lioulder-clay is a tough clay with fewer 

 stones, and abo\'e this a more sandy boulder-clay, con- 

 taining numerous boulders, overlaid by several feet of 

 stratified sandy clay without boulders; while on the sides 

 of the ridges, and at some places near the present shore, 

 there are beds and terraces of sand and gravel, constituting 

 old shingle beaches a])parently much more recent than 

 the other deposits. 



xVll these deposits are more or less fossiliferous. The 

 lower boulder-clay contains large and fine s})ecimens of 

 Zcda glacial is and otiier deep-water and nuul-d welling 

 shells, with the valves attached. The upper clay is 

 remarkably rich in shells of numerous species; and its 

 stones are covered with IVdyzoa and great Acorn-shells 

 {Balaniis Ifaineri), sonietimes two inches in diameter and 

 three inches high. The stratified gravel holds a few 

 littoral and sub-littoral shells, which also occur in some 

 places in the more recent gravel. On the surface of some 

 of the terraces are considerable deposits of large shells 



