THE EVOLUTION 

 AND DISTRIBUTION OF FISHES 



CHAPTER I 



Introduction 



It has been a generally accepted dictum with zoologists 

 during the past hundred years, and has been even more 

 emphasized during the past twenty, that animal life in 

 general and not least the great group of fishes originated 

 amid marine surroundings, and only gradually spread to- 

 ward a freshwater environment. Were one to adduce evi- 

 dence for this it might be said to include the views set 

 forth in every important manual and textbook on zoology 

 and palaeozoology, as well as in the well-known special 

 treatises and research volumes that deal with recent as 

 well as fossil fishes. And yet against such a conclusion 

 there existed many weighty observations and field studies, 

 brought forward by the very authors of the marine idea. 



The writer spent much available time during several 

 years of his student and earlier teaching days m investi- 

 gating the fossil flora and fauna of the Edinburgh region, 

 and also the stratigraphic relation of these. The area 

 covered included extensive developments of Lower Car- 

 boniferous or Calciferous sandstone rocks that extend for 

 miles westward from Edinburgh as well as across the 

 Firth of Forth into a large part of Fifeshire. It also 

 included the higher group of rocks known as the Carbon- 

 iferous Limestone that stretches in extensive beds and as 

 a great trough, from some miles east of Edinburgh across 

 into Fifeshire. Above this were the Millstone Grit and 

 the True Coal Measures, both widely developed on either 

 side of the Firth. Dura Den, of classic Old Red Sandstone 

 fame, adjoined the writer's ancestral territory, while the 

 Silurian beds of the Pentland hills came in for a share 

 of attention. 



