18 
The Diabasic Schists — II. V. Winchell. 
loose rocky slopes, d d. The cliffs are freshly scarred where* 
blocks have lately fallen; the talus is steep and barren, and 
many large blocks lie at its foot. The location of the notch i& 
such as to protect it from any exceptionally rapid erosion under 
ordinary conditions, it being a divide between streams to the 
north and south and not a water-gap; but it is closely in the 
direction of glacial movement, and a strong stream of ice 
must have been turned through this passage between the high 
enclosing hills. 
Let the preglacial profile be a a; Glacial erosion must have 
been particularly severe in such a trough, and after the pre¬ 
glacial waste had been scoured out, the bed rock must have 
been attacked and ground out to a depth of many feet, chang¬ 
ing the profile from aaa to bcb. The notch was thus deepened 
and widened, and when the ice was at last melted out of it, a 
clean U-shaped trench was revealed. Since then the small 
amount of weathering on glaciated surfaces assures us that 
there has not been nearly enough time for the talus to attain a 
form of adjustment; the first rapid, weathering by which the cliffs 
retreat from b to c has furnished the beginning of a waste- 
heap in the talus, d, below; but there is yet needed a long 
period before a new form of equilibrium, fgf, will be reached, 
such as characterizes the non-glaciated ridges. 
We may conclude therefore that we owe not only our lakes, 
our waterfalls and our gorges, but also our refreshed and em¬ 
boldened cliffs to the glacial period. Post-glacial time must 
have been brief, because so little advance has been made to¬ 
wards the more mature forms of all these features. Only the 
smallest lakes have been filled; only the weakest barriers have 
been cut away. The waterfalls have worn but a little distance 
up stream, and the gorges still retain nearly vertical walls. 
The cliffs of the New England trap-ridges show equally little 
progress towards the more conservative forms of middle life. 
September, 1888. 
THE DIABASIC SCHISTS CONTAINING THE JASPILYTE 
BEDS OF NORTH-EASTERN MINNESOTA. 
By Hokace V. Winchell. 
Several divergent theories have been presented and ably 
supported regarding the nature of the rocks associated with the 
