Geology of Lincoln Co., S. D. — Bendrat. 75 
that they had been deposited in still waters. They may with some 
rig-ht be referred to the later Tertiary and may indicate the bot- 
tom of the lake, while its shore has to be possibly sought for in 
a locality about four miles X.W. of Lennox, where borings re- 
vealed a stratum, four feet thick, of fine dry sand, as we usually 
find it on the beach. This was found at a level of about 1268 
feet above sea. Although a distinct shore line has not been 
found, having become obliterated by the Pleistocene ice sheet, 
an approximate outline can, however, be traced, aided by the 
topographic map (Canton sheet of the U. S. Geological Sur- 
vey). There might be distinguished two stages of this Tertiary 
lake, during the latter of which the lake seems to have 'extended 
along the axis of the trough towards the N.E., thus following- 
a probable sinking of the region in that direction during Plio- 
cene times. Ultimately it became obliterated, taking part in 
the general elevation of the country, which is supposed to have 
inaugurated the Quaternary. It was most probably drained 
through channels to the east, one of them, possibly the most 
important one, following the course of the present South 
Beaver creek within T.98X., R.49W., shown on the occompany- 
ing map. on which also the approximate outlines of the lake 
during [Miocene times are given. The probability of a refilling 
of the empty lake basin by glacial waters and the fprmation of a 
glacial lake, although of less extent, will be discussed later on. 
Tlic Pleistocene. 
a : Drift Sands and Gravels. 
Representing the main source of the water supply, the 
sands and gravels of the drift are found to form a stratum, 
which is not in all portions of uniform thickness, but which 
might be said to be continuous, unlike the Tertiary sands. At 
places these sands and gravels are usually deeply buried be- 
neath the till, thus, for instance, in T.iooX., R.50^^^ in sec. 35 
of Delapre township at a depth of 94 feet, and about half a 
mile west 107 feet below surface and still farther west for an- 
other half mile at a depth of 100 feet, while at little farther in 
the same direction in the S.W. corner of sec. 34 of same town- 
ship, they are found to rise to 14 feet below the surface, yielding 
a fine drinking water. On the same land is an old well dug about 
twenty-three years ago to about the same level, developing a 
strong floAv, but which was abandoned for some reason for a 
