e 
E. Andrews on the Western Boulder Drift. 175° 
in diameter, and had exactly the shape of ordinary boulders, and 
terminated abruptly on all sides in the solid clay. In many in- 
tances projecting angles near the upper parts overhung their 
ases, and in general the whole contour was such as was impos- 
sible for loose gravel to assume under the mere action of water, 
Every scientific man that saw them was convinced of two things, 
viz., that the gravel was dropped from floating ice in frozen 
masses, and that it was covered up and supported in position by 
the clay before the frozen masses had time to melt, otherwise 
the loosened pebbles would have fallen down in conical heaps. 
An unavoidable, and, at that time, a very perplexing inference 
was, that in order to support the gravel masses before they 
melted the clay must have been deposited with enormous an 
unacountable rapidity ; but later observations upon the drift 
north of us have dispelled the wonder so far as this section is 
concerned, by showing a still greater violence of water action 
in the regions from which the clay and the gravel came, as the 
following facts show. 
The state of Wisconsin is channelled with a remarkable val- 
ey. Commencing north of Lake Michigan near Lake Superior, 
this depression runs southwest and contains in its northern part 
the waters of Green Bay, and in its southern portion those of 
Rock river. It pursues an almost straight course for 400 miles 
and terminates at the Mississippi river where Rock river emp- 
ties into it 
_ From the northwest, the country descends by a gentle re 2 
into the valley, but trom the southeast it breaks down suddenly 
and often by a perpendicular precipice, as though the rocks on 
that side had been lifted along the line of a fault. rock 
ridge or rather an elevated region of Silurian rock some 300 feet 
m height, separates this valley from Lake area, % upae 
very coarse stratified, and well water-worn gravel, which for 
gan and runs southwest about two hundred miles, and be 
over 20 miles in width it covers an area of over four thousan 
