!66 The American Geologist. September, 1903. 
plished is the only conclusion that can be drawn. Stone* ap- 
plies the aptly chosen term of "plexus" to such areas, and 
characterizes them as follows : they are "the most remarkable 
of all deposits left by glacial rivers .... its surface covered with 
a jumble of heaps, mounds, cones, and ridges inclosing all 
forms of hollows, funnels, hopper-holes, kettle- holes, basins 
and Roman theatres, many of which are so deep as to inclose 
lakelets without visible outlet." Such a characterization, 
though slightly too comprehensive for the region under con- 
sideration, yet, is an accurate picture of what might obtain 
under magnified conditions. The Andover "plexus" is elliptical 
in shape, narrowing somewhat toward the southern end where 
it again assumes a more typical esker character, and a closely 
defined one. Immediately north of the delta plain and to the 
west, the feeding esker rises in elvation, broadens a little, and 
merges itself into the level topped surface of the plain. The 
plain itself is about three-quarters of a mile in diameter from 
north to south, and a trifle less from east to west. The im- 
mediate union of plain and esker, as before stated, is marked 
by a broadening of the latter, and a sharp rise in elevation. In 
this amplified area are a number of small pits, depressions, and 
kettles, from some of which there extend subsequent drainage 
lines. The portion of the feeding esker leading up to the plain, 
is very well defined for several hundred feet northward. At 
this point it has been bisected by subsidiary stream channels 
of the present Shawsheen river. Isolated sections of this esker 
are found at intervening intervals indirectly connecting the 
"plexus" area and the plain. During high water stages of the 
present stream they look like islands in a net-work of sluggish 
stream channel?, which further on find their way back to the 
main course of the river. The Shawsheen river washes the 
base of the esker on the western slope. To the northeast of the 
area containing the disconnected sections of the feeding esker, 
there is a glacial lakelet. This lakelet (Pomps pond) is a per- 
manent pond established in an ice-block hole. The water line 
in the gravels maintains its supply, and during high water in 
the river, is more or less directly connected with it. 
The surface of the plain shows a gently dipping horizon 
to the south. Its highest elevation is to the north, where the 
• U. S. G. S. Monograph 34-, 1899. 
