GLACIAL WATERS IN BLACK AND MOHAWK VALLEYS 21 



aided the melting, and eventually a section of the valley was free 

 of ice and held only the earliest of the Mohawk glacial lakes. 



We have some facts which bear on the matter of the location of 

 the weakest section of the Mohawk ice strait. The existence of 

 dritmlinlike forms on the south side of the valley and with east 

 and west direction has been recognized since the publication of the 

 Utica and Richfield Springs sheets. In 1908 Professor Brigham 

 described west-pointing drumlins in the Johnstown region (see title 

 6, page 25). In the autumn of the same year the writer determined 

 that drumlins indicating a westward flow of ice exist in perfect 

 form in the district northeast and northwest of Richfield Springs, 

 but that they terminate east of the Utica meridian. The ice-molded 

 drift forms a restricted area, mostly on and south of the line of 

 divide, about eight miles wide beginning north of Otsego lake and 

 stretching northwest to beyond Cedarville, a distance of about 18 

 miles. The drumlins are partially indicated on plate 5. 



It has been shown that drumlins are a product of the sliding 

 movement of the thinning ice edge when under efficient thrustal 

 motion of thick ice in the rear.^ The Richfield Springs drumlins 

 v/ere produced by the movement of the thinner ice on the high 

 ground, under the push of the thicker ice in the valley eastward. 

 The more remote pressure was, of course, from the Hudson valley 

 lobe. The drumlin-forming ice was an overflow from the valley ice 

 tongue. 



Here we have evidence of ice flow up the valley, from the Hud- 

 sonian lobe ; and we have proof that for a long time subsequent the 

 Ontarian lobe lay Qver the Rome district. The westward flow of 

 the Mohawk valley ice was, at this phase, probably met by the 

 opposing Ontarian ice somewhere in the Little Falls-Utica district. 

 The locality of the meeting between the two ice tongues, in the later 

 phase, would probably be the place of subsequent separation. 



The question is now pertinent : Why did the Hudson ice push so 

 far westward up the Mohawk valley, meeting the Ontario glacier 

 much more than half way, while at a later time the Ontarian lobe 

 lingered over Rome, at the west end of the valley, when the Hudson 

 valley in the Schenectady district was clear of ice ? The explanation 

 seems to lie in the form and the relative altitude and cross section 

 of the St Lawrence and the Champlain-Hudson valleys. When the 

 ice body was thick over both the Champlain-Hudson and the St 



1 Drumlins of Central Western New York. N. Y. State Mus. Bnl. iii, 

 p. 429. 



