MESOZOITEC CHANGES IN FAUNAL GEOGRAPHY. 371 
ent periods of geologic history, and the probable changes in 
physical geography that accompanied and caused this shifting of 
relations. The Mesozoic era has been taken as.a basis because 
the taunas ob that time are better known, and because the 
physical geography of that time has been better worked out all 
over the earth. But the changes which preceded the Mesozoic 
era will also be outlined as far as they are known. And since 
California is intimately connected with other regions of the West 
Coast, these regions will also be considered in so far as they 
concern California. 
PRE-CARBONIFEROUS RELATIONS. 
Cambrian and Silurian.—The Cambrian and Silurian of Cali- 
fornia, as described by Professor C. D. Walcott? in the papers cited 
below, are too little known for any opinion about them to be 
decisive; they are, however, probably like the Cambrian and 
Silurian as it is known in Nevada and the West in general. 
Devonian.—In California the Devonian is little known, 
having been described by J. S. Diller and Charles Schuchert? 
from only a few places in Shasta and Siskiyou counties, and the 
forms that occur there give little clue to the affinities with other 
regions. But from the study of the faunas of other parts of 
America we get some light on the geography of the Devonian. 
The work of Dr. A. Ulrich3 has made it clear that during 
the Lower and Middle Devonian the faunas of North America 
were closely related to those of Bolivia, Brazil, the Falkland 
Islands, and South Africa, but that they were different from those 
of Europe. But Professor H.S. Williams+ has shown that at the 
beginning of the Upper Devonian in North America there came 
in many species whose ancestors are not found in the Middle 
Devonian of that region. This fauna, however, is closely related 
Am. Jour. Sci., III. Series. Vol. XLIX., pp. 14(-144, and Bull. Geol. Soc. Amer., 
Wolk, JWDL., jd B70. 
2 Am. Jour. Sci., III. Series, Vol. XLVII., pp. 416-422. 
3Beitrage zur Geol. und Pal. von Sitidamerika, I. Palaozoische Versteinerungen 
aus Bolivien. 
4 Bull. Geol. Soc. Amer., Vol. I., Cuboides Zone and its Fauna, and Proc. A. A. A. 
S., 1892, Sec. E., Address; Scope of Paleont. and its Value to Geologists. 
