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 
