462 THE POPULAR SCIENCE MONTHLY. 



have yielded forms of old affinity, the existence of which has hitherto 

 been unsuspected. The general character of the group of star-fishes 

 embedded in the white chalk is almost the same as in the modern 

 Fauna of the deep Atlantic. The sea-urchins of the deep sea, while 

 none of them are specifically identical with any chalk-form, belong to 

 the same general groups, and some closely approach extinct cretaceous 

 genera. 



Taking these facts in conjunction with the positive evidence of the 

 existence, during the Cretaceous epoch, of a deep ocean where now 

 lies the dry land of Central and Southern Europe, Northern Africa, 

 and Western and Southern Asia ; and of the gradual diminution of this 

 ocean during the older Tertiary epoch, until it is represented at the 

 present day by such teacupfuls as the Caspian, the Black Sea, and the 

 Mediterranean; the supposition of Dr. Thomson and Dr. Carpenter 

 that what is now the deep Atlantic was the deep Atlantic (though 

 merged in a vast easterly extension) in the Cretaceous epoch, and that 

 the Globigerina mud has been accumulating there from that time to 

 this, seems to me to have a great degree of probability. And I agree 

 with Dr. Wyville Thomson against Sir Charles Lyell (it takes two of 

 us to have any chance against his authority) in demurring to the as- 

 sertion that " to talk of chalk having been uninterruptedly formed in 

 the Atlantic is as inadmissible in a geographical as in a geological 

 sense." 



If the word " chalk " is to be used as a stratigraphical term and 

 restricted to Globigerina mud deposited during the Cretaceous epoch, 

 of course it is improper to call the precisely similar mud of more re- 

 cent date chalk. If, on the other hand, it is to be used as a mineralo- 

 gical term, I do not see how the modern and the ancient chalks are 

 to be separated ; and, looking at the matter geographically, I see no 

 reason to doubt that a boring-rod driven from the surface of the mud 

 which forms the floor of the mid- Atlantic would pass through one con- 

 tinuous mass of Globigerina mud, first of modern, then of tertiary, 

 and then of mesozoic date ; the " chalks " of different depths and ages 

 being distinguished merely by the different forms of other organisms 

 associated with the Globigerince. 



On the other hand, I think it must be admitted that a belief in the 

 continuity of the modern with the ancient chalk has nothing to do 

 with the proposition that we can, in any sense whatever, be said to be 

 still living in the Cretaceous epoch. "When the Challenger's trawl 

 brings up an Ichthyosaurus, along with a few living specimens of Be- 

 lemnites and Turrilites, it may be admitted that she has come upon a 

 cretaceous " outlier ; " but a geological period is characterized not only 

 by the presence of those creatures which lived in it, bijt by the absence 

 of those which have only come into existence later; and, however 

 large a proportion of true cretaceous forms may be discovered in the 

 deep sea, the modern types associated with them must be abolished 



