RECESSIONAL ICE BORDERS IN BERKSHIRE, MASS. 345 



The Yokun river drains the ravine, and the little lake may be 

 known as Yokun glacial lake. It is near 1,350 feet above sea- 

 level, while the top of the terrace at Lenoxdale is close to 1,020 

 feet. The base of the terrace is about 960 feet, and this is taken 

 as the basis of measurement. The distance is about four miles 

 from the central part of the terrace to the nearest part of the 

 Yokun glacial lake. Hence the rate of slope along the side of 

 this ice-tongue was nearly 100 feet per mile. 



Several other tongues within the area studied afforded similar 

 evidence, but generally the rate of slope indicated was slightly 

 greater, between 100 and no feet in a mile. This rate was used 

 as the basis for interpolating from the ends of tongues up to the 

 re-entrant angles at their sides, and has seemed to give satis- 

 factory results. The rate of slope is a little greater where 

 tongues are very narrow, and a little less where they are broad. 

 The average slope along the side of the Hudson lobe, regardless 

 of the tongues and re-entrants, is something between twenty- 

 five and thirty feet per mile. 



In the Olean^ and Salamanca quadrangles Leverett found 

 the side slopes of tongues which reach down the ravines to the 

 Allegheny river to vary between 100 and 130 feet per mile, or 

 slightly steeper than those here reported for the Berkshire 

 region. 



Salisbury found the slope at the ice-front at Baraboo, Wis., 

 to be 320 feet per mile. Other estimates of slope quoted by 

 him are for the surface of the ice at points some distance back 

 from its edge, where the slope is always less than at the front. ^ 



THE CONTINUOUS AND SEPARATE INDIVIDUALITY OF THE RECES- 

 SIONAL ICE BORDERS. 



The remains of the ice-borders in the Berkshires are mostly so 

 faint and so fragmentary, and the fragments are so scattered 

 about in the valleys and on the hillsides, with so little appear- 

 ance of order or arrangement, that a map showing these features 

 alone is unintelligible; it appears for the most part like a mere 



' Pocket map in Monograph XLI, U. S. Geol. Surv. 



'" Glacial Geology," Geol. Surv., New Jersey, Vol. V, pp. 41-3. 



