18 The Diabasic Schists— H. 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 is 
such as to protect it from any exceptionally rapid erosion under 
ordinary conditions, it being a divide between streams to tlie 
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^vveathering 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 HoBACE V. Winchell. 
Several divergent theories have been presented and ably 
supported regarding the nature of the rocks associated with the 
