ATLANTIC OOZE 77 



they are a great factor in the building-up of this 

 world, and, in reasoning from appearances, we are led 

 to say that they have been so from very remote times. 

 Should it be conclusively shown that the vast chalk 

 beds of Europe and Asia have been laid down by the 

 shells of ancient globigerina, we shall understand one 

 of the grandest of geological problems. It is but fair 

 to say there are some students of Nature who do not 

 accept the theory that the chalk of the formations 

 with which we are acquainted in various parts of the 

 world was laid down by globigerina similar to those 

 now found in the Atlantic. Able men like Jeffreys, 

 Murray, and Renard, consider chalk to have been laid 

 down in shallow waters, or on the borders of a con- 

 tinent, rather than in deep ocean areas. 



Their opinions receive support, in a measure, from 

 the fact that globigerina ooze contains a large per- 

 centage of silica, while chalk is nearly pure carbonate 

 of lime. The chalk, however, contains many flint 

 nodules. If at great depths, in ancient times, the 

 silica of the chalk was dissolved, and taken up by 

 glass sponges, the purity of the chalk would be 

 accounted for. In support of this, there have been 

 times when the solvent power of ocean waters was so 

 great that arragonite organisms entirely disappeared 

 from certain beds now forming limestone. The 

 Challenger naturalists found that globigerina and 

 pteropod ooze were completely dissolved below certain 

 depths. Carbonic acid would, no doubt, play an 

 important part in bringing about such changes. Dr. 



