3i8 The American Geologist. ^'^^'^ ^9'^=^- 
imum distance of about twenty-five miles. Salisbury writes of tbis 
older drift as follows : 
■'Tbe extra-morainic glacial drift is far from constituting a contin- 
uous sbeet within the area where it occurs. A large part of the sur- 
face has no drift, and where it occurs it is often very meagre, being 
represented only by scattered bowlders derived from formations farth- 
er north. Thin beds of drift, two or three feet in depth, are common, 
while in not a few places' the drift is of considerable thickness, locally 
as much as thirty feet. 
"The lack of continuity of drift in this region is in striking contrast 
with the condition of things north of the moraine, where drift in great- 
er or less thickness is essentially continuous. It is true that there are 
frequent outcrops of rock north of the moraine ; and it is true that 
there are, here and there, areas of some size where the drift is thin. 
But the areas where the drift is very thin are much less extensive north 
of the moraine than south of it. The relationship may be expressed 
in some such terms as the following : North of the moraine, four- 
fifths of the surface is so deeply covered with drift as to conceal the 
underlying rock, and the products of its decay ; south of the moraine' 
and north of the drift limit, four-fifths of the surface is nearly free 
from drift. Just as the one-fifth north of the moraine has occasional 
bowlders and small patches of drift, so the four-fifths of the area south 
of the moraine, and north of the drift limit, has occasional bowlders, 
and small amounts of drift in other forms. The amount of drift per 
square mile on the four-fifths to the south is probably less than the 
amount on the one-fifth to the north." 
Both here and in Kansas the outermost drift appears to the writer of 
this review to be of less antiquity than is supposed by Salisbury. From 
the amount of subaerial erosion which he thinks to have been effected 
by the rains, rills, and large streams, since the deposition of this drift, 
he concludes that it is far more ancient, as fifteen or twenty times older, 
than the terminal moraines and their inclosed drift sheet, which belong 
to the Wisconsin stage of the Glacial period. Although the outer drift 
is demonstrably the older, its age seems to me to be very likely no 
greater than four or five times the age of the Wisconsin drift. The 
decayed condition of the rock fragments in the outer old drift may be 
due to erosion from surfaces of pre-glacially decayed bedrocks ; and 
the inequalities of distribution of that drift may be of similar charac- 
ter with the very irregular accumulation of the later drift on areas of 
drumlins. Originally patchy drift accumulation outside the boundary 
of the later drift in New Jersey appears more probable than isolation 
of the drift deposits by subsequent erosion. w. u. 
