1891.] 
317 
[Davis. 
On motion of Professor Hyatt it was voted that in accepting 
the resignation of Mr. Dexter the Society express its regret at 
the necessity for his action and the hope that his health may soon 
be restored. 
November 18, 1891. 
President G. L. Goodale in the chair. Fifty-nine persons 
present. 
Dr. George Baur gave an account of his visit to the Galapagos 
Islands. Chatham, the most eastern of the islands, was reached 
June 9th, and during the following months all the islands south 
of the equator, with the exception of Narborough, were visited. 
Large collections were made. The collections and observations 
seem to prove the continental origin of the islands. The harmo- 
nious distribution of the animals proves that these volcanic islands 
are but the tops of volcanic mountains of a greater area of land 
which has sunk below the level of the ocean. All the islands were 
formerly connected, forming a single large island ; through sub- 
sidence the single island was divided into several islands. The 
conditions on the various islands being different, each island pro- 
duced its peculiar races. 
It is highly probable that a large continent formerly spread out 
where to-day we find the Pacific ocean. 
Another result anticipated by Dr. Baur, when his collections 
shall have been fully worked up, is that the change of the species 
can be followed stage by stage on the different islands. 
Variation goes on in definite lines determined by the environ- 
ment ; the surroundings are the most important factors of varia- 
tion, natural selection plays a secondary part. 
Prof. W. M. Davis said that he could not accept Dr. Baur’s 
conclusion that because the islands were once united to one 
another they were also united to the mainland ; the probability of 
the great oceanic and continental changes seems even more 
doubtful. 
The minimum depth between the several islands measures the 
amount of emergence by means of which they will be brought 
into a single large volcanic island. This is much less than the 
