28 Evolution and Distribution of Fishes 



pressions must have been much shallower however than the 

 often deep and at times ravine-like inequalities of the ocean 

 bed now, that is confined within and between hard and 

 thick sub-oceanic rock-floors. Instead, therefore, of the 

 exposed land and water surfaces being as now, in the pro- 

 portion of I to 3, it seems almost assured that a ratio of 

 2 in land to 5 in sea would be a conservative estimate. Such 

 a configuration is set forth to some extent by Freeh in 

 "Lethaea geognostica." 



The land masses, however, in virtue of the plastic 

 character of the earth's crust, must seldom have been ele- 

 vated above sea level to more than 3000 or 3,500 ft., 

 and even over more extensive areas must have been com- 

 paratively level, like the eastern part of Central Brazil 

 and the Congo basin of West Africa now. 



Owing also to frequent inequalities and localizations 

 in deposition of material, with resulting surface stresses, 

 or from shifting of bodies of freshwater owing to volcanic 

 strains and upheavals wide expanses of freshwater must 

 often have extended in the form of lakes, swamps and slug- 

 gish rivers. These — as will be explained later — seem to have 

 formed often as wide expanses only a few feet above the 

 sea level. So when crustal disturbances took place, an 

 invasion by the sea of such freshwater expanses must often 

 have caused a sudden and marked change in floral or faunal 

 characters, that we can frequently read the record of, alike 

 from the altered nature of the rock-forming deposits, and 

 the remains of fossilized organisms. The converse re- 

 sult would naturally happen when slight elevations of 

 shallow sea-bottoms caused sudden destruction of marine 

 life, and the ushering in of a lacustrine, or swamp, or terres- 

 trial vegetation. 



The above do not represent vague or hypothetical en- 

 vironal changes, but are exactly required by, and exactly 

 conform to, all the evidences before us, when we investigate 

 the early fossiliferous rocks, and not least the fish and 

 other organisms enclosed in these. In line also with the 

 studies of Joly ( 11; 23) on the solution and transfer of 

 salt from decomposing rocks, and its gradual accumulation 

 in the sea under constant evaporation action, it should be 



