384 THE JOURNAL OF GEOLOGY. 
In the Lower and Middle Jura there was no connection with 
European waters through the Pacific region, but rather through 
the Atlantic or ‘Central Mediterranean Sea”’ of Neumayr, bring- 
ing a central European fauna. 
Near the beginning of the Upper Jura this connection with 
European waters was cut off, and one established with those of 
Siberia and northern Europe, bringing in a Boreal fauna. 
This same connection was continued through part of the 
Lower Cretaceous, giving a Boreal fauna to the Knoxville. 
‘Near the beginning of the Gault, connection with the Boreal 
sea of Russia was cut off, and communication established with 
southern India and through that country with central and south- 
ern Europe, bringing in a warm-water fauna. This connection 
existed during the greater part of the Cretaceous, but after this 
time the faunas are confined much more closely to their present 
ranges, although even today many of our living and Tertiary 
mollusca are found in Japan. 
These changes in faunal geography are too widespread and 
easily correlated over great areas to be charged to mere moun- | 
tain-making; they must rather be of the nature of continental 
uplift and subsidence. A study of these changes will throw 
light on the problem of the extinction of faunas and explain the 
great poverty of certain beds, in which the conditions for life 
seem favorable. 
The fauna of California has not been a genetic series, but 
rather a succession of independent faunas, derived by migration 
from various parts of the earth, complicated by the mixture 
with the products of local development. Therefore the student 
that would intelligently study the genesis and history of this 
fauna must not neglect the fossil records of any region, since all 
may have contributed some elements to this complex assemblage 
of forms. 
JAMES PERRIN SMITH. 
STANFORD UNIVERSITY, 
CALIFORNIA, 
