608 LE. CHAM BE RIELN, 
the upper Indus and Ganges basins, involving the site of the 
present Himalayas, and this appears to have been preéminently 
a transition tract from the Paleozoic to the Mesozoic eras.t The 
adventitious factor in such cases becomes a saving clause so far 
as the efficient preservation of remnants of the previous fauna is 
concerned. But even the adventitious factors receive their 
importance from their critical relations to the systematic atti- 
tudes of land and sea upon which chiefly depend the great lines 
of progress of marine life. 
T. C. CHAMBERLIN. 
1GRIESBACH, Mem. Geol. Surv. India, Vol. XVIII, pp. 1-232, 18901. 
