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



theory principally on the harmonic biological relations which 

 exist between the different islands of the group. In brief Dr. 

 Baur's theory was that the islands had all been connected with 

 each other at some not remote geological period, and at a still 

 earlier period had been attached to the North American con- 

 tinent, possibly in the region of Central America. This view 

 has been supported by some naturalists and vigorously opposed 

 by others. During the year our party remained on the islands 

 excellent opportunities were offered to study the situation from 

 an impartial stand-point, and after having made a careful study 

 of the collections of plants formed on the different islands, the 

 author is led to a view concerning their origin which is slightly 

 at variance with both of the above theories. 



If these islands are continental in origin, as was maintained 

 by Dr. Baur, one would naturally expect to find a close faunal 

 relationship between them and the mainland, a condition, how- 

 ever, that does not exist. There are neither large mammals 

 nor batrachians, both of which should be present in greater or 

 less quantity if the islands had been connected with the main- 

 land within even comparatively recent geological times. Fur- 

 thermore, with the exception of the large land tortoises, which 

 are found on most of the larger islands of the group, the fauna 

 is about what one would expect to find on almost any group 

 of oceanic islands. 



It might be maintained that during the great volcanic dis- 

 turbances that have taken place since the islands were sep- 

 arated from the mainland, both the mammals and batrachians 

 were exterminated. While this might be true as far as the 

 mammals are concerned, it would hardly be true for the 

 batrachians, as they would very likely be able to withstand as 

 adverse conditions as the reptiles, and it is hardly probable 

 that a combination of circumstances would come about which 

 would obliterate one of these groups and leave the other in a 

 more or less flourishing condition. 



One of the strong arguments in favor of a former land 

 connection is the presence on the islands of the well-known land 

 tortoises, which are rather closely related to certain fossil 

 tortoises from some of the later geological formations of North 

 America. The presence of land tortoises on the islands is not 

 so difficult to explain as it appears to be at first sight. While 



