1897.] The Geological Congress in Russia. 951 
tion” leaves a very large field of determinate evolution entirely 
uncovered and unexplained, and there remains a tertium quid 
which requires further investigation. Determinate evolution 
in these non-plastic structures at present strikes me as part of 
the mechanical necessities of development, if I may so express 
it. That is, given a certain primitive form, there is only one 
route along which it can attain a certain end, provided the 
intervening stages are mechanically effective. It is some such 
law of mechanical necessity as this which out of the conical 
type of reptilian teeth has evolved first the triconodont type, 
the tritubercular, and finally the multitubercular, and from 
these main stages have arisen sub-stages which are repeated 
and independently acquired over and over again in different 
branches of the mammalian class. This is not an explanation, 
or a theory, it is a fact yet to be understood. 
Organic Selection constitutes a distinct advance, and is, at 
least, a very useful working hypothesis, but it is by no means 
the conclusion of the whole matter, as Alfred Wallace main- 
tains. We must persevere in our analysis of life processes ~ 
as revealed in living organisms and in fossils with a perfectly 
open mind, perhaps for many decades, perhaps for another 
century, before we reach final conclusions in regard to the 
complex processes of evolution. 
Columbia University. 
THE GEOLOGICAL CONGRESS IN RUSSIA. 
By CHARLES PALACHE. 
The Seventh International Geological Congress assembled 
in St. Petersburg during the first week of September, 1897. 
The Congress was notableamong the meetings of this organ- 
ization for the large number in attendance. It will certainly 
be memorable, to such of its members as took part in them, 
for the extent and interest of the excursions planned in con- 
