282 Canadian Record of Science. 



boniferous in Belgium and in the United States of America. 

 In the Carboniferous and Permian they are few and small, 

 and they do not culminate till the Cretaceous, in which 

 there are no less than ninety-one so-called species in Amer- 

 ica alone ; but some of the largest known species are found 

 in the Eocene. The oyster, though an inhabitant of shal- 

 low water, and very limitedly locomotive when young, has 

 survived all the changes since the Carboniferous age and 

 has spread itself over the whole northern hemisphere. 1 



I have collected fossil oysters in the Cretaceous clays of 

 the coulees of Western Canada, in the Lias shales of Eng- 

 land, in the Eocene and Cretaceous beds of the Alps, of 

 Egypt, of the Eed Sea coast, of Judea, and the heights of 

 Lebanon. Everywhere and in all formations they present 

 forms which are so variable and yet so similar that one 

 might suppose all the so-called species to be mere varieties. 

 Did the oyster originate separately on the two sides of the 

 Atlantic, or did it cross over so promptly that its appear- 

 ance seems to be identical on the two sides ? Are all the 

 oysters of a common ancestry, or did the causes, whatever 

 they were, which introduced the oyster in the Carbonifer- 

 ous act over again in later periods ? Who can tell ? This 

 is one of the cases where causation and development — the 

 two scientific factors which constitute the basis of what is 

 vaguely called evolution — cannot easily be isolated. I 

 would recommend to those biologists who discuss these 

 questions to addict themselves to the oyster. This familiar 

 mollusk has successfully pursued its course and has over- 

 come all its enemies, from the flat-toothed selachians of the 

 Carboniferous to the oyster-dredgers of the present day, has 

 varied almost indefinitely, and yet has continued to be an 

 oyster, unless indeed it may at certain portions of its 

 career have temporarily assumed the guise of a Grypha?a 

 or an Exogyra. The history of such an animal deserves to 

 be traced with care, and much curious information respect- 

 ing it will be found in the report which I have cited. 



But in these respects the oyster is merely an example of 



1 White, Report U.S. Geol. Survey, 1882-83. 



