96 The Ajnerican Geologist. February, iqod 
iterate my assertion that the mineral deposits are invariably 
found in or closely connected with faults of a system much later 
than that which is represented by the great dislocations of the 
strata such as the Keating, Lawrence and Trinity Centre faults 
which are of the same age as the general folding of the meta- 
morphic strata and of the injection of granite-porphyry dike 
material. The gold-bearing faults are also later than all the 
intrusives except probably the newer system of dioryte-porphy- 
ryte dikes. They are gold-bearing independently of what for- 
mation they may cut. Locality is of more importance than for- 
mation. With possibly the exception of the deposits in connec- 
tion with the quartz-porphyryte dikes, the gold was derived 
from a great depth, ascended as heated solutions, and was de- 
posited along the veins through a great vertical range. The 
age of this action was subsequent to the formation of the di- 
oryte-porphyryte dikes of the earlier system, which cut the 
Mariposa slates of late Jurassic age. The mineral veins were 
formed and the surface portion eroded before the Shasta-Chico 
series of late Cretaceous sediments were deposited. Hence, 
they belong to some portion of early Cretaceous time. 
NEW LIGHT ON THE DRIFT IN SOUTH DAKOTA.* 
By J. E. Todd, Vermillion, S. D. 
Hitherto, the writer's study of the drift of South Dakota 
has led him to consider it to belong mainly, if not entirely, to 
•the Wisconsin epoch. The reasons briefly stated are as fol- 
lows: 
(a) The numerous borings made in the state for artesian 
wells, have nowhere revealed distinctly, well defined forest- 
beds or soils, such as are found in some other regions. Though 
limited sheets of sand have been found in till at certain points, 
it has not been clearly proved that they are not such as might 
have been formed by sub-glacial streams or a slight advance of 
the ice-sheet during a single period of occupation. A few 
exposures described herein in the eastern part of the state have 
thrown some doubt upon this point. 
*The first edition of this paper was read at the 1898 meeting of the 
Iowa Academy of Sciences and published in their Proceedings for that 
year. 
