No. 1.] DAWSON — POST-PLIOCENE. 39 



The Saxicava sand sometimes rests on the Leda clay or Boulder- 

 clay and sometimes directly on the rock, and the latter is often 

 striated below this deposit ; but in this case there is generally 

 reason to believe that Boulder-clay has been removed by denuda 

 tion. 



4. Terraces and Inland Sea Cliffs. 



These are closely connected with the deposits last mentioned, 

 inasmuch as they have been formed by the same recession of the 

 sea which produced the Saxicava sand. At Montreal, where 

 the isolated mass of trap flanked with Lower Silurian beds, 

 constituting Mount Koyal, forms a great tide-guage for the re- 

 cession of the Post- pliocene sea, there are four principal sea mar- 

 gins with several others less distinctly marked. The lowest of 

 these, at a level of about 120 feet above the level of the sea at 

 Lake St. Peter, may be considered to correspond with the general 

 level of the great plain of Leda clay in this part of Canada. On 

 this Terrace in many places the Saxicava sand forms the surf ice, 

 and the Leda and Boulder-clay may be seen beneath it. This 

 may be called at Montreal the Sherbrooke Street Terrace. An- 

 other, the Water-work Terrace, is about 220 feet high, and is 

 marked by an indentation on the Lower Silurian limestone. At 

 this level some Boulder- clay appears, and in places the calcareous 

 shales are decomposed to a great depth, evidencing long sub- aerial 

 action. Three other Terraces occur at heights of 386, 440, and 

 470 feet, and the latter has, at one place above the village of Cote 

 des Neiges, a beach of sand and gravel with Saxicava and other 

 shells. Even on the top of the Mountain, at a height of about 700 

 feet, large travelled Laurentian boulders occur. On the Lower 

 St. Lawrence, below Quebec, the series of Terraces is generally 

 very distinctly marked, and for the most part the lower ones are 

 cut into the Boulder and Leda clays, which are here of great 

 thickness. I give below rough measurements of the series as they 

 occur at Les Eboulements, Little Mai Bay and Murray Bay, 

 where they are very well displayed. I may remark in general 

 with respect to these Terraces, that the physical conditions at the 

 time when they were cut must have been much the same with 

 those which exist at present, the appearances presented being very 

 similar to those which would occur were the present beach to be 

 elevated. 



