—— Ee Se 
GOLDTHWAIT: SAND PLAINS OF GLACIAL LAKE SUDBURY. 269 
Physiographic Features which mark Water-Planes in an 
Ice-Front Lake. 
The features which one may look for as evidence of an extinct ice-front 
lake are briefly these : — 
(a) Suors-Lings, marked by beaches and bars, or by escarpments and 
benches, built by the waves of the lake wherever the material is non- 
resistant enough, the exposure great enough, and the level of the lake 
permanent enough. Benches and bars of this sort are wonderfully well 
developed along the shores of the great lakes of the ice age, like Bonne- 
ville and Agassiz; they are easily traced along the shores of Lakes 
Chicago, Algonquin, Warren and Iroquois; and they are fairly well 
shown in New England in the Contocook valley near Hillsboro, N. H. 
(6) Ourter CHANNELS, cut across cols or spurs by overflowing waters, 
wherever the material was weak enough and the outlet was main- 
tained long enough. -The remarkable dry gorges of Lake Warren, 
near Syracuse, N. Y., are fine examples of outlet channels (Fairchild ; 
a, b, c, d, e, f). Another is the valley of the Illinois River, cut by the 
outlet of Lake Chicago. 
(c) Laxe Borrom Deposits. The finer clays and silts which are fed 
into the lake will be carried far out, and may settle to form a horizon- 
tally stratified deposit. Silt deposits of this nature have been described 
by Upham in his accounts of glacial Lake Agassiz (d, 20-25). 
(d) Devras. Wherever a stream enters one of these lakes, there is 
opportunity for a delta to form, provided the supply of waste is too rapid 
or too coarse for the waves of the lake to wash it away, and provided 
there is time enough. These deltas are large features in Lake Agassiz 
(Upham; a, d); and in the New York lakes described by Fairchild 
fine deltas were built where outlets from one lake entered the next 
(Fairchild ; e, 38, 39, 52, 59). 
(e) Sanp Dettas, or Sanp Puatns. These are deltas of a special 
class, and of such importance in New England that they deserve separate 
treatment. A brief description and discussion of them follows. 
Sand Plains—their Form and Structure. 
Sand plains are delta-like deposits of sand and gravel, built out from 
the ice into standing water at its front. The fact that gravels swept 
out from the melting ice occur thus, in isolated patches, rather than in 
a vaguely continuous sheet over the whole region, indicates that the 
