SOME GLACIAL WASH-PLAINS. 



79 



lins, eskers, kames and terraces, in the classification of 

 glacial deposits. 



So far as glacial drainage repeats the conditions exist- 

 ing in ordinary streams and rivers, we shonld expect to 

 find, at the months of rivers and streams dischaiging from 

 the ice, alluvial deposits corresponding in all essential re- 

 spects to deltas with lobate and multilobate mai-gins, to 

 alluvial cones and fans, and to confluent cones and fans. 

 The examination of the region here described has revealed 

 examples analogous to most of these 

 types, difiering only in the respect that 

 the deposits were built against or in the 

 presence of an ice formation instead of 

 a rock formation and that, by the melt- 

 ing of the ice, anomalies in the to- 

 pography have been introduced which 

 separate the group, often widely, from 

 those deposits of non-glacial origin. 



The following classes of glacial stream 

 deposits are here recognized under the 

 head of extraglacial wash : 



Wash-plains, comprising gently slop- 

 ing areas of gravel and sand deposited 

 along the ice front. They are divisible 

 into kinds dependent on their relations 

 to frontal moraines, the ice-margin, and 

 to the ice-margin and eskers. 



From their relations to frontal moraines there arise over- 

 wash-plains banked up against the outer edge of the frontal 

 moraine. 



From their relation to the ice-margin alone there arise : 



a. Frontal moraine terraces, with an ice-contact slope, 

 charged with till and boulders, a true morainal deposit. 



b. Frontal terraces, like the preceding but lacking the 

 till-coating along the ice contact. 



' fMlie . 



Fig. 1. Contour map 

 of the Say les vil le 

 esker-fan (area left 

 white) in Rhode Isl- 

 and. Horizontally 

 ruled areas, swamps; 

 black areari, ponds ; 

 dotted areas marginal 

 terraces of sand and 

 gravel. (Topography 

 from Providence atlas 

 sheet, U. S. Geological 

 Survey.) 



