SOME OLACfAL WASH-PLAINS. 89 



Plains of the terminal moraine, — The largest and best 

 defined outwash plains in this region are those lying in 

 front of the outermost or terminal moraine lyino; upon 

 the New England Islands. Tho plain on Long Island has 

 not yet been mapped. If a plain ever existed in front of 

 the morainal accumulations on Block Island, it has long 

 since been washed away by the sea. The })lains of Mar- 

 tha's Vineyard and Nantucket' are well illustrated by the 

 contour maps of the U. S. Geological Survey. These 

 two plains are apparently contemporaneous, having been 

 formed well within a reentrant angle of the ice-front lying 

 between lobes, for convenience designated as the Cape Cod 

 and Narragansett Bay lobes, which were more sharply de- 

 fined when the ice front lay north of the New England 

 Sounds on the " back bone " of the Cape. 



Nantucket plain. — The Nantucket plain (13) is an 

 essentially eskerless, kameless, well-defined outwash delta 

 or series of fan cones fed by streams coming from the 

 glacier, the position of whose front is very clearly marked 

 by the terrace at the northern margin of the plain. Near 

 its head, the plain attains elevations of sixty feet above 

 the present sea-level, these points, apparently marking the 

 last layers of outwashed gravel and sand, being separated 

 by furrows due either to the failure of adjacent fans to 

 coalesce marginally, or, as can be proved in some cases, 

 to creases marking the discharge of subglacial streams. 



The former contact of this plain with the ice-front can 

 be traced by alignment to Tuckernuck Island on the west, 

 and so onward by the wave- washed isle of Muskegct, to 

 Chappaquiddick island where small fans extend in a north- 

 west line towards the larger island of Martha's Vineyard. 



Nantucket presents us with perhaps the best and clear- 



' Consult the Nantucket, Muskeget, Martha's Vineyard and Gay Head atlas 

 sheets (in Massachusetts). A colored model of Nantucket on the scale of one 

 mile to the inch has been prepared by Mr. G. C. Curtis of Brookline, Maes. 



