380 REVIEWS 
characteristic class of formations of the Rocky Mountain Tertiaries. 
During recent years not a few geologists, here and there, have 
expressed a disposition to regard some of the deposits usually assigned 
to lakes as the products of stream action or “sheet wash,” or of a 
combination of these with lake deposition. To the reviewer, who is 
among these dissenters, the favorite illustration of such modes of 
deposition is the present and recent accumulation in the Great Valley 
of California where several forms of subaérial aggradation are con- 
joined with lacustrine and marine deposition. This newer mode of 
interpretation has been applied to a notable series of formations dis- 
tributed at intervals from the Medina, and even the Keweenawan, to 
the Lafayette and the recent deposits of the great basins of all the 
continents, particularly the arid basins. The great red terranes, with 
their associated products of desiccation and saline concentration, 
especially, have seemed to the reviewer attributable to such combined 
action, since a basin of saline concentration carries in its very terms 
the idea of a basin of detrital lodgment whose central part may be an 
area of subaqueous deposition but whose border is almost inevitably a 
zone of subaérial accumulation. The doctrine of non-lacustrine basin- 
aggradation, as it lies in the mind of the reviewer, has its most dis- 
tinctive application to tracts of relative aridity, for it is in these, 
chiefly, that the conditions of subaérial lodgment preponderate over the 
conditions of subaqueous deposition, except in the case of aggrading 
river bottoms near base level which are undergoing a depression of 
gradient by deformation. In an arid basin-tract the precipitation is 
likely to be greatest on the elevated rim, and there it is often spas- 
modic, taking the form of cloudbursts and similar intensified forms. 
The gradient is also highest, as a rule, in the rim zone. These form a 
combination of agencies which result in an exceptional transportation 
of detritus down the slopes of the basin rim followed by a marked 
reduction of power of transportation as the flatter part of the basin is 
reached; for there the flood loses its power by lowered gradient, by 
spreading, by absorption, and by evaporation. Deposition is the 
usual consequence. In a humid region, the conditions are largely 
reversed; the streams augment in volume as they flow over the basin- 
plain and the power of transportation is more or less fully maintained. 
If the basin be a closed one the accumulated waters arising from the 
excess of precipitation over evaporation soon cover the basin floor with 
a lake which occupies the territory that in an arid region would be 
