100 THE POIKILITIC PERIOD. 



it is worth calling to mind that enormous physical changes great 

 displacements of land and sea preceded in each case the deposition 

 of the only two extensive and abundant stratified deposits of red 

 oxide of iron known in Europe. One later case occurs, indeed, at 

 the base of the chalk of Yorkshire, Lincolnshire, and Norfolk, and 

 for that a similar supposition has been proposed. 



To complete the retrospect, we have only to call attention to 

 the well-established fact of the paucity of fossils in the purely red 

 beds ; their comparative rarity, or even total absence, in the purple 

 beds ; and their abundance (even contemporaneous abundance) in 

 the grey beds. Was marine life very rare in the directions from 

 which the red streams flowed ? Was the fine red mud hostile to 

 the growth of mollusks and corals, by impeding the action of the 

 respiratory organs ? Or, finally, were the sediments brought down 

 by great rivers like the Mississippi and its branches, and so neces- 

 sarily almost devoid of oceanic life? We may adopt such a 

 conjecture as the last with no great hesitation, and it agrees in 

 some degree with the ingenious supposition of Mr. Godwin Austen, 

 without requiring, as he does, that the sediments should have been 

 deposited in a lake of fresh water. 



