RECESSIONAL ICE BORDERS IN BERKSHIRE, MASS. 343 



We have seen in Fig. 4 a good illustration of the work of 

 border drainage. The stream which made this channel was 

 larger than most border streams within the Housatonic quad- 

 rangle, for it was the outlet of a temporary lake which filled the 

 Monterey valley and drained a considerable area of land and ice 

 lying to the northwest. None other equal to this was found, 

 but there are good records of border drainage along the base of 

 Peru hill east of Hinsdale ; three miles directly south of Tolland ; 

 south of Mill River and from New Marlboro south and south- 

 west ; along the hill east of Sheffield; north of Salisbury and 

 northeast of Hillsdale, N. Y. West of the quadrangle splendid 

 lines of border drainage run southwest from Brainard, from East 

 Chatham, and from near Spencertown. 



In the Taconic quadrangle, so far as investigated, border 

 drainage was found particularly strong where the ice-front rested 

 against the Green mountains between Bennington, Vt., and Wil- 

 liamstown, Mass. It is strong also between North Adams and 

 Cheshire along the flank of Hoosac mountain. 



But some of the finest examples of border drainage are those 

 associated with the later outlets of Lake Hoosic. As soon as 

 the retreating ice-front withdrew from the north end of the 

 Rensselaer Grit plateau, Lake Hoosic found lower levels of dis- 

 charge in that vicinity. At four or five successive halts the out- 

 let river found a new and lower course to the southwest along 

 the front of the ice, and in each position it made a well-defined 

 channel, and built a sandy delta each time where it struck the 

 level of the Hudson estuary. 



INTERPOLATION BETWEEN MORAINE FRAGMENTS. 



The study of the ice-border in certain localities, where either 

 border drainage or the lateral as well as the terminal moraines 

 were traceable, has furnished the basis of a rule for interpolating 

 re-entrant angles around hills and mountains from one terminal 

 deposit to another. One of the best examples showing this 

 relation may be seen in the Housatonic valley south of Pitts- 

 field. The apex of this tongue rested at Lenoxdale, and at this 

 place there is a very conspicuous terminal deposit. A small 



