148 LIGHT SCIENCE FOR LEISURE HOURS. 



reach these creatures, we have no present means of 

 determining. 



If there is one theory which geologists have thought 

 more justly founded than all others, it is the view that 

 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, how- 

 ever, 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.'* 



Even more interesting, perhaps, 'to many, are the 



* This opinion Dr. Carpenter has 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 

 as respects adjacent deposits. 



