212 



MR. E. J. GAEWOOD & DR. J. W. GREGORY [May 1 898, 



that which forms the esker, ruas along each side of the valley at 

 the same height. (See fig. 5.) 



Fig. 5. — Sketch-plan and sections of the esker-like gravel-ridge. 



■ Section along CD. — - 



Section along A. B : 



■ Scale of Yards — 



4-0 60 80 700 



— I — 1 — I — 1 I I I 



An examination of the valley in which this interesting gravel- 

 ridge occurs leaves no doubt as to its mode of origin. At one time 

 the mouth of the valley was blocked by a ridge of Carboniferous 

 cherts which converted the middle part of the valley into a lake- 

 basin. The streams filled this basin with gravel washed from the 

 great terminal moraine in the upper part of the valley. Later on, the 

 Esker Valley river cut through the chert-bar, and then the streams 

 began the erosion of the gravel-plain. The esker has been left in 

 the angle between the stream which comes from Brent Pass and a 

 tributary which drains the southern slope of the Trident. 



This explanation, of course, does not apply to all eskers. The 

 reasons given by Prof. Sollas ^ for rejecting this origin of Irish 

 eskers are conclusive for most cases. But, as Mr. J. B. Woodworth "^ 

 reminds us, ' the term esker is applied in common usage to deposits 

 having at least slightly different modes of origin,' and ' each esker 

 should be diagnosed on its own merits.' 



^ W. J. Sollas. * A Map to show the Distribution of Eskers in Ireland,' Sei. 

 Trans. R. Dubl. Soc. ser. 2, vol. t (1896) p. 786. 



^ J. B. Woodworth, ' Some Typical Eskers of Southern New England,' 

 Proc. Boston Soc. Nat. Hist. vol. xxvi (1894) p. 219. 



