174 E. Andrews on the Western Boulder Drift. 
of magnificent drift sections, both modified and unmodified. 
Besides there are’ over fifty railroads which have cut the hills 
in every direction, and innumerable wells, coal shafts, tunnels, 
and river erosions, making in all probably 2000 linear miles of 
drift section exposed to observations. It is impossible to mis- 
take the meaning of the facts, and the result has been to oblige 
those western geologists most familiar with the sections to 
abandon the glacier theory and admit that the boulder drift of 
this region is altogether an aqueous deposit, though the waters 
floated vast quantities of ice. 
It has often been stated that the only stratified drift is 
that which has been rearranged by water since its first deposit. 
This rule entirely fails in the west, the original drift being 
clearly stratified. I ought to remark that the distinction be- 
tween the two is easily made out by the form of the surface. 
Original drift is marked by a peculiar style of undulation, and 
by the frequent occurrence of circular and oval valleys without 
any outlet. Modified drift arranges all its excavations wit 
reference to lines of drainage, and its valleys all have outlets. 
The eye once educated +o these distinctions will rarely com- _ 
mit an error in deciding between the two. Now the stratifica- 
tion, with its beds of clay, sand, gravel, etc., is often just 28 _ 
clear in the original drift as in that which is modified, and even” 
jthe summits of lofty hills show both stratification and — 
be necessary. The city of Chicago pushed a tunnel for two 
miles in the unmodified boulder clay beneath Lake Michigan for 
