SOME GLACIAL WASH-PLAINS. 



79 



litis, eskers, kftmes and terraces, in the classification of 

 glncial deposits. 



So far as glacial drainage repeats the conditions exist- 

 ing in ordinary streams and rivers, we shonld expect to 

 find, at the mouths of rivers and streams discharging fiom 

 the ice, alluvial deposits corresponding in all essential re- 

 spects to deltas with lobate and multilobate margins, to 

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

 The examination of the region here descriljed has revealed 

 examples analogous to most of these 

 types, diftering 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. 



'/MUe 



The following classes of glacial stream 



Fig. 1. Contour map 

 of the Saylesville 

 eskerfan (area left 

 white) In Rhode Isl- 

 anil. Horizontally 

 ruled areas, swamps; 

 black areas, ponds; 

 dotted areas marginal 

 terraces of sand and 

 gravel. (Topography 

 from Providence atlas 

 sheet, U. S. Geological 

 Survey.) 



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-coatino- alons: the ice contact. 



