352 THE CANADIAN NATURALIST. ' [Sept. 



This fact (if as a fact it is finally established by further 

 researches) may throw considerable light upon its origin. 



This fossiliferous boulder clay may represent the debris 

 accumulated on its progress downwards from the mountain by the 

 descending glacier, and deposited by it, as it pushed itself beneath 

 the sea on reaching the shore. 



While this boulder clay possesses the general physical charac- 

 teristics of the boulder clay first described — containing the usual 

 striated and polished stones, and being compact and unworkable 

 — these characteristics may, perhaps, fairly be described as not 

 quite so intense in their development in many cases, although often 

 its only distinguishing mark is the presence of shell fragments. 



Its peculiar position in cliifs near the shore, the occurrence 

 of fossils, and its general composition, seem to sustain the theory 

 that it marks the point where the debris of great glaciers was 

 pressed to the bottom of the sea at the final point of their descent. 



Without reference, however, to the method of its formation, 

 as a matter of fact there exists a boulder clay. (1) Fossiliferous 

 — the included shells being arctic in character, but fragmentary- 

 (2) Chiefly developed in the neighbourhood of the shore in the 

 form of sea cliffs. (3) Physically the same as that which un- 

 derlies the shell clay of the Clyde district, although sometimes 

 distinguishable by a diminution in the intensity of its charac- 

 teristics. 



III. The type of a third clay, which may in its extreme form 

 be termed a boulder clay, may be seen near Lag, Ai'ran, overlying 

 the older boulder clay. It is very hard and compact ; the shells 

 are better preserved than in the second boulder clay : but the 

 embedded stones are not so well striated, and have been more or 

 less worn since their first glaciation. Patches of sand and sandy 

 clay are common. 



This clay I am disposed to regard as the wash of the last 

 described boulder clay upon a somewhat exposed coast. The 

 angular blocks have been jumbled together, and their striations 

 half obliterated, and their polish somewhat worn off, while the 

 clay has been washed and rewashed around them, and a rude and 

 rough habitat formed for the scanty development of some forms of 

 molluscan life. 



IV. An upper boulder clay, belonging to the period of 

 retreating glaciers, and an ameliorated climate, is very distin- 

 guishable. (1) It is far less compact than any clay yet described. 



