Geology of Lincoln Co., S. D. — Bendrat. "jc} 
The history of this complex sand-and-gravcl stratum of the 
drift is read in general outlines about as follows : There was 
a time of floods and torrents, steadily increasing in transporting 
power, followed by a cessation, of quiet accumulation of finer 
materials, of aeolian action upon dry sands and of soil form- 
ation and vegetation to some extent. This was succeeded by 
another time of floods and strong currents, which, however, lost 
their swiftness in the course of time, until there was inaugurat- 
ed another interval of rather quiet accumulation, which was in 
turn succeeded by relatively longer and shorter periods of 
stronger and weaker activity, until the till became deposited. 
The material of the stratum apparently displays a great 
variety of rocks of igneous as well as of metamorphic and 
sedimentary nature. 
Of the ingredients of the drift in the blufTs on the Big Sioux 
the following may be noted : 
Cobblestones of 3x2^, 3x2, 2^2x1^ inches in size, of feld- 
spatic granite, carrying titanite, the mica being of inferior quan- 
tity, while the orthoclase at places very beautifully exhibits the 
laminar cleavage structure. Pink granite of less stability, dis- 
integrating, the mica plates, however, being recemented by 
calcium carbonate, which partly coats the stone. The quartz 
grains and teklspar crystals are of about the same size and the 
percentages of the three ingredients are nearly equal. 
Gneiss of dark gray color with brownish, greenish and red- 
dish shades, coated to some extent by lime ; at some places the 
surface is rendered somewhat cavernous by the removal of the 
feldspar. The quartz as well as the feldspar is of medium size, 
while the n'ica at places has been altered into chlorite, only iso- 
lated traces of the original mica being preserved. The rock 
is of considerable hardness. Crystalline limestone (Silurian) 
of gray color passing into lighter and darker yellow shades 
and exhibiting in some instances striae, which run parallel to 
each other, and also spicules of sponges and fragments of grap- 
tolites. 
Pebbles from 2x1^ to lyixj^ inches in size, of dioryte of 
dark color with darker and lighter shades of green and brown, 
with large and showy plagioclase feldspar crystals and the 
hornblende very conspicuous ; quartz-dioryte of somewhat brit- 
tle texture and dark color, carrying besides titanite some minute 
