ee Distribution of Land Birds. [ZOE 
has pointed out, the islands formed a part of the mainland at the 
beginning of the Quaternary Epoch. This has been proved in 
various ways, particularly by the discovery of mammoth remains 
on one of them, indicating that the separation must have occurred 
during or just previous to the glacial period ; showing, in fact, as 
Prof. Le Conte has said, that these islands are all that remains of 
what once constituted the Coast Range, the intermediate land hav- 
ing been lost by subsidence. In pre-glacial times all California, ap- 
parently, was inhabited by forms from the Sonoran Province, which 
were isolated upon these islands at the time of subsidence, and 
thus kept distinct from the northern horde driven south by the ice, 
which spread over all other parts of the State. Isolation would 
thus, to a considerable degree, tend to preserve these pre-glacial 
forms to the present day, as to a vastly greater degree it has pre- 
served the primitive forms of Madagascar. The botanical basis for 
this theory is as follows: The flora of these islands consists largely 
of peculiarly Californian species, together with a considerable num- 
_ ber of endemic forms, and is characterized by the absence of north- 
ern and eastern species found on the mainland. 
The most conspicuous feature of the flora is its distinctively south- 
ern character, as compared with the adjacent coast. Since Prof. 
Le Conte’s paper was written, the flora of the islands has been more 
fully and carefully examined, and Mr. T. S. Brandegee has shown * 
that the number of species peculiar to the islands is much less than 
was formerly supposed. This, however, does not in any way alter 
Prof. Le Conte’s theory, but merely shows that the isolation has not 
been sufficiently long continued, or sufficiently complete perhaps, to. 
produce the degree of differentiation at first ascribed to them. Mr. 
Brandegee has also called attention to the fact that the tempera- 
ture of the islands is higher than that of the adjacent coast}, which 
would be another factor in accounting for the presence of southern 
forms. This much at least remains, that the flora of the islands is 
southern in character, and possesses certain peculiar features; more- 
over, that it has not to as great a degree that admixture of northern — 
forms characteristic of the mainland floras. All these facts are in 
complete accord with the theory that the present flora is the rem- 
nant of an earlier and more widely distributed one which has been 
preserved by isolation. 
i 
* Zoe, i, p. 129. t Zoe, i, p. 109, 
