38 TOPOGRAPHIC DEVELOPMENT OP KLAMATH MOUNTAINS, [bull. 190. 
Now, there is little doubt that during the Pliocene, as well as at present, there was 
a marked difference between the contemporaneous faunas of the San Diego region 
and of northern California and Oregon. From these facts it follows that the Plio- 
cene of northern California, if it exists, would be difficult to determine by paleon- 
tological comparison with that of San Diego, and might comprise an almost totally 
distinct series of species. Furthermore, no reliable lists of the Merced (Pliocene) 
or the Monterey (Miocene) faunas of the middle part of the State have been made 
public, and the condition of the fossils generally leaves much to be desired. 
Lawson has made a study of the geomorphology of the region near Rio Dell, 
from which the fossils sent by Mr. Diller are largely derived. He regards them 
as Pliocene, the identifications being due to Dr. John C. Merriam. Paleontologic 
data alone are of value to determine the relations of a given horizon to the general 
geologic column. In the present case the fossils comprise a large number of spe- 
cies which are similar to recent forms, and have usually, as in Dr. Merriam's list, 
been assumed to be identical with the recent forms they resemble. If the deter- 
mination of age be made by the method of percentages of surviving forms, it is 
obvious that they will show on these assumptions a percentage sufficient to justify 
the reference of these beds to the Pliocene, as has been done. On the other hand, 
if these fossils are merely prototypes and not identical, this will reverse the deter- 
mination and put the fauna in the Miocene. 
I confess to strong doubts as to the specific identity of many of the forms in 
question with their recent analogues. The Rio Dell fossil fauna contains a cer- 
tain number of species also found in the Empire beds, and some of the most com- 
mon species are also common at Coos Bay, but as a whole the fauna is markedly dif- 
ferent. It is not only different in the census of species as a whole, but it repre- 
sents a more northern or colder water assemblage. Indeed, the whole fauna bears 
a striking resemblance to the existing fauna of the Gulf of Alaska, of which it is 
beyond question a precursor. 
Now, the Alaskan Unga beds and the Oregonian Empire beds agree in possessing 
many species in common and in having a warm temperate facies. They are 
doubtless contemporaneous, and certainly Miocene. We have in the Rio Dell 
fauna, then, a record of a marked change of temperature and an incursion of 
northern species, because it is not credible that a warm-water fauna could exist 
in Alaska coincidently with a cold-water fauna in California. I feel confident, 
then, that the Rio Dell fauna is younger than the Empire beds fauna. On the 
other hand, the Pliocene of southern California represents much more typical 
conditions than the subsequent Quaternary or the antecedent southern Mio- 
cene, just as the Floridian Pliocene does for the Floridian region. Many species 
now known only in the Gulf of California lived at San Diego during the Pliocene. 
It is probable, then, that the presence of the boreal fauna at Rio Dell represents 
a cold interval between the time of the Empire beds and the Pliocene properly so 
called. 
The fossils of Rio Dell are contained in a sandstone that is usually pretty tough 
and often very hard. There is no Pliocene fauna known to me which occurs in a 
rock so indurated as this. Moreover, the color of the matrix is, when unaltered, 
of the bluish tint which is almost characteristic of the Miocene everywhere in 
America. 
The genus Lyropecten is characteristic of the Miocene all over the temperate 
regions of the globe. A splendid species (L. dillerl Dall) occurs at Rio Dell. No 
Lyropecten has so far been reported from any positively Pliocene horizon. This 
species is the analogue of the P. madisonius of the Chesapeake Miocene, as the 
P. crassicardo Conrad of the San Pablo Miocene horizon of middle California is 
the analogue of the P. jeffersonius of the Chesapeake Atlantic Miocene. 
On the other hand, some of the species at Rio Dell are identical with species of 
the Merced Pliocene horizon near San Francisco. 
