Geology of Lincoln Co., S. D. — Bcndrat. 89 
west of the latter town. A scries of four of about equal hight 
above the level of Long creek have been met with along the 
eastern bank of said creek about seven miles south of Lennox, 
the summits of which are to some extent flattened and covered 
with the biggest bowlders, seen by the writer within the limits 
of the area. They suggest a phase of transitionary cessation 
during the retreat of the glacier and might possibly have 
formed a portion of a barrier, that at least contribute(> some- 
thing to the formation of a glacial lakelet, which is supposed 
to have reoccupied the once abandoned basin of the Pliocene 
lake. The possible western boundary of this glacial lake has 
been indicated by Todd on his "Geological Map of a Portion of 
Eastern South Dakota" in Irrigation Paper Xo. 34 of U. S. 
Geological Survey, while its eastern shore line from the 97" 
on is found approximately given on the map subjoined to this 
paper. It is the outline of the probable extension of the lake 
eastward, after it had removed a portion of its barrier. 
The bowlders, however, although they are found widely dis- 
tributed over the region under discussion, represent one of the 
most prominent features of the moraine in so far as they are 
most frequently found on its summit as well as on its slopes. 
They are usually more angular in shape than those found in the 
till, while their size varies from 3^2 foot to 4 and even 5 feet in 
diameter. Although there seems to prevail a decided irregular- 
ity in the distribution and the arrangement of these erratics, 
there are points, especially in the northern part of the region, 
on the back as well as on the inner slope of the moraine, where 
the bowlders, especially where they cross the road and also in 
pastures at both sides of the road, can be observed to be ar- 
ranged in trends, which maintain an average direction from 
the X.W. to the S. E. or straight north and south. This pe- 
culiar arrangement has been indicated on the map. They are 
crowded on the inner slope and less thickly strewn over the 
back of the northern ridge, while they are more feebly devel- 
oped in the middle portion of the region, except on the drum- 
lins. mentioned above, and entirely lacking in the southwestern 
piivt of the area, reappearing within the limits of the southern 
member of the Altamont moraine. Distinct striation of the 
surface has been observed only in one case. viz.. on a light 
yellowish, very hard limestone, ixi foot in size, of probably 
