INDICATIONS OF UPHEAVAL AND DEPRESSION. 117 



in the fauna of India. Reeling's Island is an atoll in the middle of 

 the Indian Ocean, which may have some connection with the ancient 

 continuity which existed between the Mazarine region of Eastern 

 Africa and the Malay Archipelago. In the Pacific, the chief atolls are 

 the Low Archipelago, Gilbert Islands, Marshall Islands, and Caroline 

 Islands. 1 



It is thus seen that atolls extend in lines like fringing reefs and 

 barrier reefs with which they alternate. If, then, fringing reefs occur 

 chiefly in areas of upheaval and other reefs in areas of depression, the 

 Pacific and Indian Oceans exhibit to us by these means corrugations 

 of the ocean floor which are now in progress, insensible it may be in 

 amount during the periods for which they have been observed, but 

 obviously analogous to the changes of level, of which the strata and 

 existing contours of land are demonstrative evidence. If the atolls 

 exist in great synclinal folds which are in process of depression, the 

 lands bordered by fringing reefs are as certainly in the position of 

 great anticlinal folds undergoing upheaval. To the physical geologist 

 the distribution of coral reefs in the strata presents an important 

 factor in elucidating the relations of Land and Water while de- 

 posits were accumulating, especially in the Tertiary, Cretaceous, and 

 Jurassic periods. 



1 See Map in Danvin's Coral Reefs. 



