368 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



The fact that each of the five great mountains of Albemarle 

 seems to have been the original home of one of these five races, 

 suggests that these volcanoes formerly were separated by 

 water and formed five islands. These five islands must have 

 remained separate long enough to permit the development of 

 the differences which distinguish the five kinds of tortoises 

 now found upon Albemarle. Then these five small islands 

 must have been elevated until they merged to form the present 

 Albemarle Island. 



If there has been such an elevation of Albemarle Island in 

 recent times, we might hope to find some record of it in the 

 rocks, either in the form of fossils or of elevated beaches. Mr. 

 Ochsner, the geologist of our expedition, found such evidence ; 

 but, since his results have not yet been published, I shall con- 

 tent myself by calling attention merely to Heller's statement: 



"Near Iguana Cove, Albemarle, there are several old 

 sea-cliffs now situated a considerable distance inland. At 

 Tagus Cove on the same island a series of terraces, still con- 

 taining the characteristic cavities made by sea-urchins, are 

 now several hundred feet above the present sea-level." 



This is positive proof of the recent elevation of Albemarle 

 Island, and favors our explanation of the presence of several 

 species of tortoises upon this island. 



Our studies of the reptiles of the Galapagos Archipelago, 

 therefore, all point to the conclusion that these are not oceanic 

 islands. We must regard the present islands as made up of 

 the higher portions of a much more extensive land-mass which 

 formerly existed in this region. This Galapagos Land was 

 the home, probably, of one race of giant tortoises, of one kind 

 of gecko, of one species of Tropidurus, of two kinds of 

 iguanas, and of two species of snakes. Gradual depression 

 resulted in the submersion of much of this Galapagos Land. 

 As the lower portions were covered by water the higher parts 

 became, at intervals, separate islands, inhabited, after isolation, 

 by the same kinds of reptiles which had occupied them before. 

 Variation through a long period of time produced specific and 

 sub-specific changes in these isolated colonies of reptiles, until 

 each island upon which tortoises remained sustained its own 

 peculiar kind. Similarly, the snakes, the gecko, and the 

 Tropidurus, of various islands became differentiated. Since 



