20 NATURAL SCIENCE. July. 



below it, to the thickness of the depth of subsidence ; and some of 

 the sediments were calcareous, making now thick limestone strata. 



" After the Cretaceous period, and in the Pliocene Tertiary 

 chiefly, or the Tertiary and Glacial period, the whole region of the 

 Rocky Mountains was elevated ; the elevation was 16,000 feet in 

 part of Colorado, 10,000 feet, at least, in the region of the Sierra 

 Nevada, 10,000 feet in Mexico, and over 17,000 feet in British 

 America, latitude 49° to 53°, and less to the north. The region of the 

 Andes, at the same time, was raised to a maximum amount of 20,000 

 feet; the Alps, 12,000 feet; and the Himalayas, 20,000 feet. Moreover, 

 at the close of the Champlain period there was another epoch of smaller 

 elevation, introducing the recent period. These elevations, affecting 

 a large part of the continental areas, could not have taken place 

 without a counterpart subsidence of large areas over the oceanic 

 basin ; profound oceanic subsidence was hence in progress during 

 the growth of coral-reefs. The subsidence cannot be questioned." 



In these remarks Dana has forcibly dwelt on the facts which 

 greatly weigh with geologists in inducing them to accept the " subsi- 

 dence-theory " of coral-reefs. That the questions involved in the 

 explanation of the numerous examples of coral-reefs in different 

 oceans are much more complicated, than was at one time suspected, 

 they freely admit ; but with such clear evidence as they possess of 

 subsidence and deposition having gone on concurrently, until deposits 

 thousands of feet in thickness were piled up, geologists find it difficult 

 to believe that coral growth was the one form of organic accumulation 

 that did not conform to this common rule. Important and valuable, 

 then, as were the observations made upon coral-reefs by the officers 

 of the " Challenger," geologists still feel that many more exact studies 

 of these wonderful structures require to be made, before the problems 

 connected with their origin can be considered as finally settled. 



John W. Judd. 



Chemico-Biological Changes in the Ocean. 



The investigations conducted by the " Challenger " Expedition 

 with reference to the distribution and composition of oceanic deposits 

 over the floor of the ocean have led directly to a number of inter- 

 esting researches, undertaken with the view of throwing some light 

 on the chemical changes now taking place in the ocean under the 

 influence of organisms and organic matter. The results are contained 

 in a series of papers by Murray, Irvine, Woodhead, Young, Gibson, 

 and Anderson, published in the Proceedings and Transactions of the 

 Royal Society of Edinburgh, from 1888 to 1894. 



These researches appear to explain some of the phenomena 

 connected with the distribution of calcareous and siliceous organisms 

 in different depths and regions of the ocean, as well as certain 

 peculiarities of the different varieties of deposits. The results of 

 these investigations may be briefly summarised. 



A series of experiments were carried out with hens and crabs in 

 order to determine whether or not they were dependent on the 



