In Carboniferous and Permian Epochs 137 



CHAPTER V. 



The Physical and Biological Environment of Fishes. 

 (b) During the Carboniferous and Permian Epochs. 



In the Carboniferous and Permian as in the Siluro- 

 Devcnian systems freshwater and marine strata, both 

 often of great thickness, have to be distinguished, though 

 it is difficult as yet to correlate these exactly over the world. 

 But in the Northern Hemisphere, over a great part of 

 Europe and North America, probably also of Russian 

 Siberia, a fairly continuous land-area must have persisted 

 from "Old Red" times. For only thus can we interpret 

 the plant and animal organisms encountered in the rocks. 

 Here also it may at once be emphasized, that during the 

 Mid-Carboniferous — possibly somewhat earlier — we first 

 trace the invasion of marine areas by evolving lithe fresh- 

 water fishes belonging to the great elasmobranch series. 

 But a truly remarkable feature is that these become practi- 

 cally exterminated again over such areas, in late Carboni- 

 ferous or in early Permian days. 



In the Carboniferous formation as a whole, two im- 

 portant groups of rocks are largely — often wholly — of 

 freshwater or land origin. The lowermost of these has 

 been variously called the Culm, Calciferous Sandstone, 

 Misslssippian (In N. America) or Lower Carboniferous, 

 and its beds evidently extended continuously from Central 

 North America, eastward through north Britain and 

 France, to Mid Germany and Mid Russia. Chronological- 

 ly this series seems to have been formed over the North 

 Atlantic and Nearctic continents of Freeh — both of which 

 must have been more or less continuous as Indicated by 

 him — at a time when further south In Europe, and also in 

 North America, the marine beds of the Lower Carbonifer- 

 ous or Misslssippian, were in process of deposition. So 

 while the latter contain a great wealth of typical marine 



