30 Evolution and Distribution of Fishes 



The most emphatic query however — likewise from the 

 geological side — is that of Chamberlin in his paper "On 

 the habitat of the early vertebrates" (/J; 400) as well as 

 in many sections of the textbook of which he is joint author 

 {8; II). In the former, his opening paragraphs were evi- 

 dently influenced by earlier descriptions of Newberry and 

 Orton for "Corniferous" beds, and their supposed marine 

 origin. Detailed reference is made to this in subsequent 

 pages of the present work (p.p. 126, 129). Later, in his 

 "Geology" he says {8; II; 482) regarding the Devonian, 

 — "The general faunal conception is, that in the Appala- 

 chian tract and in the Canadian provinces lying to the 

 north-east of it, as well as in Great Britain and Russia, 

 there were many lodgment basins that were progressively 

 filled by land-wash and freshwater sediments, and that 

 these basins were the home of a freshwater or brakish- 

 water fauna, in which ostracoderms and fishes were the 

 leading elements, and crustaceans their chief colleagues." 

 And again he remarks under "the Mississippi period" 

 (P- 535)'- "Fish appear to have first effectually invaded 

 the open sea in the Devonian period, but during that period 

 true marine fishes seem to have been inferior in number and 

 variety, to those of the inland waters." 



Elsewhere, and in another work, the writer hopes also 

 to quote the modified or limited view expressed by J. M. 

 Clarke as to the origin and distribution of the eurypterids, 

 and which advocates the existence of wide freshwater areas 

 in which these giant arachnids disported. 



In succeeding chapters of this work, the question is 

 fully discussed by the writer, on the ground of evidence 

 there adduced. But for a proper understanding of the 

 evolution of fishes in relation to their environment, the 

 following seem to be requisite conditions: — (a) the earth's 

 crust was then in a relatively plastic state; (b) as a con- 

 sequence, the land and sea were more uniformly distributed 

 than now; (c) high land elevation and deep ocean beds were 

 as yet alike absent; (d) extensive and connected freshwater 

 areas existed, and permitted wide migration and resulting 

 dispersion of freshwater organisms, not least of nemerteans 

 and fishes; (e) the extended and fairly uniform distribution 



