ORIGIN OF SCAURS 335 



foi' Ypsilanti, Michigan, liowever, shows the forms referred to in unusual 

 detail, admirable scaurs occurring at the two points where the road 

 toward Eawsonville on the left bank comes nearest to the river less than 

 2 miles from town. As scaurs are but slopes too steep for vegetation, the 

 character of the vegetation is an important element in their occurrence. 

 In general, the larger the growth, the stronger the root, the better the 

 slope resists slipping, even when the foot is actively undermined. A 

 grassy slope begins to break up as soon as the foot is washed by a stream, 

 but a slope overgrown with shrubs resists much longer. One in trees is 

 very resistant. Such a one occurs on the right bank of the Huron river 

 about 2 miles southeast of Ypsilanti. The trees are well grown and well 

 enough rooted to carry the ground with them in great blocks 20 by 30 

 feet, as they incline, some one way, some another, on their uncertain foot- 

 ing. Eents between the blocks afford basins that fill with every rain, 

 until last year the inclination of the trees and lack of parallelism in their 

 trunks was more noticeable than any cracking or slipping of the earth. 

 The strain has become too great for them, and the slope will before long 

 become bare. Had it not been for the trees, the slope would have been 

 bare long ago. 



The abundance of stripped bluff, or scaur, must vary with the develop- 

 ment of the valley. A young stream has its whole bank in scaur. As 

 scrolls of flood-plain develop on either hand the bluff above assumes a 

 moderate angle of slope and begins to grass over. With a wide flood- 

 plain comes a general grassing of the bluffs. The spots of stripped bluff 

 are survivors of an earlier condition. As the scaur has its foot consumed 

 rapidly by the stream while the grassy bluff is most stable below, steep- 

 ness is almost as characteristic of scaurs as their bareness. Prom these 

 considerations we may expect much inequality in the extent to which 

 scaurs occur along streams, yet in a sufficient number of examples we 

 should expect to find as many on one side as the other. 



The author's attention was first called to scaurs on the lower Eouge in 

 1903, when, with Mr Isaiah Bowman, he counted their occiirrence to 

 ascertain what proportion of the valley was now subject to the widening 

 process. We found this to be 10 per cent; but Mr Bowman at once 

 noticed that two-thirds of them occurred on the right-hand side of the 

 river, and this uniformly for many miles. He suggested the deflection 

 due to terrestrial rotation as a possible explanation. It has long been 

 believed that streams should show some tendency to bear to the right from 

 this cause. It has not usually been possible to show that this tendency 

 has perceptible effect. A note was published in Science for January, 



