146 LIGHT SCIENCE FOR LEISURE HOURS. 



the various strata of the earth were formed at different 

 times. A chalk district, for example, lying side by 

 side with a sandstone district, has been referred to a 

 totally different era. Whether the chalk was formed 

 first, or whether the sandstone existed before the minute 

 races came into being which formed the cretaceous 

 stratum, might be a question. But no doubt existed 

 in the minds of geologists that each formation belonged 

 to a distinct period. Now, however, Dr. Carpenter 

 and Professor Thomson may fairly say, 'We have 

 changed all this.' It has been found that at points 

 of the sea-bottom only eight or ten miles apart, there 

 may be in progress the formation of a cretaceous 

 deposit and of a sandstone region, each with its own 

 proper fauna. * Wherever similar conditions are found 

 upon the dry land of the present day,' remarks Dr. 

 Carpenter, < it has been supposed that the formation of 

 chalk and the formation of sandstone must have been 

 separated from each other by long periods, and the 

 discovery that they may actually co-exist upon adjacent 

 surfaces has done no less than strike at the very 

 root of the customary assumptions with regard to 

 geological time.' l 



Even more interesting, perhaps, to many, are the 

 results which have been obtained respecting the varying 

 temperatures of deep-sea regions. The peculiarity just 

 considered is, indeed, a consequence of such varia- 



1 This opinion Dr. Carpenter Las since somewhat modified. It 

 will be remembered, of course, that the evidence derived from the 

 nature of superposed strata is in no way affected by what is shown 

 above to hold with adjacent deposits. 



