160 RANGE OF GRAPTOLITES. [CH. Ill 



That this may have been so is suggested by two con- 

 siderations deduced from two classes of facts. In the first 

 place the former wider range of organisms than now is 

 well known. This has been held to imply a former pre- 

 dominance of more uniform conditions of temperature 

 and climate, but it may also perhaps be looked upon as 

 evidence of another kind, which we shall now enter into. 

 I quote from Prof. Heilprin's manual the fact that out 

 of 13 Silurian and 24 Devonian Brachiopods found in the 

 deposits of China 10 of the former and 16 of the latter 

 occur in European formations, a proportion which is not 

 only very striking, but almost inexplicable on the hypo- 

 thesis that the conditions of marine life in the several 

 regions were then precisely as now. 



Another example may be taken from the Graptolites. 

 This is a particularly useful example, for it enables us to 

 make use of the dilemma. It has been suggested that 

 the Graptolites flourished in deep water and that the 

 rocks which contained them are therefore true deep-sea 

 deposits. If this is admitted, then the question is settled 

 at once without any necessity to proceed further. But 

 if not, we have to account for the striking fact that out 

 of the 24 species of Graptolites from Australia no less 

 than 18 are species belonging to Canada and the United 

 States. 



Now we may contrast with the conditions that ob- 

 tained during the Palaeozoic period those which obtain 

 at the present day. And the contrast is most thorough. 

 Prof. Heilprin remarks that out of "the 400 or more 

 species of molluscs inhabiting the Japanese waters it 



