ae ic 5.) 
ee 
~ 
Geology and Natural History. 315 
becomes 250. The review of the fossil invertebrates is by the 
well-known paleontologist Dr. C. A. ite. 
Mr. Collett has increased much the value of the volume by the 
insertion of a colored geological map of the State, compiled from 
the labors of the former State Geologist, Mr. Cox, and those of : 
other workers in Indiana geology. 
5. fossils as a criterion of Geological equivalency.—The 
uncertainties connected with the use of fossils as a criterion of 
geological age was the subject of the able address before the 
geological section of the British Association at Montreal by its 
Tr. 
in the northwestern Himalaya, and of Sind; those pertaining to 
the fossils, chiefly plants, of the Gondwana system of India, and 
those of the coal-measures of Australia and the Karoo beds of 
South Africa, Mr. Blanford states objections to the commonly 
received view with regard to the approximate universality of 
faunas, floras and climates in ancient time, and concludes with 
the following recapitulation. 
(1) That the geological age assigned on homotaxial grounds to 
the Pikermi and Siwalik mammalian faunas is inconsistent with 
the evidence afforded by the associated marine deposits. 
(2) The age similarly assigned on the same data to the different 
series of the Gondwana system of India is a mass of contradic- 
tions; beds with a Triassic fauna overlying others with Rhetic 
or Jurassic floras, 
(3) The geological position assigned on similar evidence to 
between the faunas and floras of distant lands have probably been, 
t eater than the differences between the 
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has an 
€rroneous in so large a number of cases that no similar deter- 
™inations should be accepted unless accompanied by evidence 
from marine beds. It is probable in many cases—perhaps in the 
. 
