STUDIES FOR STUDENTS. 4QgI 
with those of northern Europe, Lytocerasand Phylloceras are \ack- 
ing in the latter region. Also in the lower part of the California 
Knoxville beds the above mentioned genera_are unknown, and 
come in only higher up where the first members of the tropical 
Indian fauna began to come in. 
Water barriers—By far the greater part of marine animals 
live near the shore, and are unable to exist under other con- 
ditions. To these an abysmal sea is as impassible a barrier as a 
continent. But an east-west sea affords good opportunity for 
passage from one side to the other simply by slow progress 
along the margin. The fauna of the Mediterranean is a good 
evidence of this, the animals on the European shores not differ- 
ing appreciably from those on the African. 
And even on the opposite sides of great north and south 
oceans there are usually many species in common; the Atlantic 
shore American fauna has many European species, and the 
Pacific shore harbors many from Asiatic waters. Their passage 
was effected in most cases along continental borders that have 
since been obliterated by subsidence and erosion. We have an 
abundance of independent geologic evidence that such recent 
changes have taken place, for example the destruction of the 
Antillean continent since Tertiary time, as worked out by Dr. 
JE AWes Spencer. 
No doubt just such great recent changes in the distribution 
of land and water could be worked out in the Indian ocean, by 
application of the same method of study. The studies of 
Neumayr,? Waagen3 and Suess# have demonstrated the existence 
of a continent in that region during late Paleozoic and early 
Mesozoic times, connecting Australia with Asia.. 
By a study of the geographic distribution of animals Wallace5 
has shown that in comparatively recent times Australia was 
™ Bull. Geol. Soc. Am., Vol. VI., 103-140. 
? Geographische Verbreitung der Jura formation. 
3 Palzontologia Indica. 
4 Antlitz der Erde. 
5 Geograph. Distrib. Animals, Vol. II., The Australian region, pp. 387-485. 
