Meeting of the American Asssocintion. — Uphnm. 219 
a whole, there are more bits of lamellibranch shells and casts of the in- 
terior than anything else in the referable fragments; next to these in 
point of numbers come the tests of foraminifers; then follow echino- 
derms, corals, bryozoans, and gastropods. Although the foraminiferal 
genus OrbitoideH does not seem to Ije represented iu the samples from 
depths above 900 feet, there seems to be no particular change in the 
rock, in ascending order, until a marked transition appears between the 
samples from 700 and 675 feet. 
In view of these facts the author is inclined to place the approximate 
upper limit of the Vicksburg beds of the Eocene in this well at 700 feet 
below the surface. The lower limit of the Vicksburg may not have been 
reached. Orbitoides seems to be the predominating foraminifer down 
to 1,450 feet. Between that depth and the next below there is a decided 
change in color, and, while Orbitoides does not entirely disappear at 
-once, two conical forms referred to Textidai-ia become much more nu- 
merous. Below 1,875 feet Orbitoides seems to be absent. 
Above 700 feet the material was so comminuted, probably by the 
drill, that it seems impracticable to differentiate the Miocene and Plio- 
cene. The massive limestone at 50 feet may. however, mark the ap- 
proximate upper limit of the Pliocene. 
This paper was discussed by Profs. LeConte. Hitchcock, Stevenson, 
and Rice. 
i*. The Hydraulic Gradient of the Main Artesian Basin of the NoiiJi- 
west. J. E. Todd. After giving a brief statement of the extent and 
attitude of the Dakota sandstone formation and the general distribution 
of the wells deriving their waters from it, attention was directed espe- 
cially to the remarkable fact that, when reliable readings of closed 
pressure are compared, there appears to be a quite regular decline in the 
pressure hight from west to east, which may be compared to the hy- 
draulic gradient of a stream. The most complete series yet obtained is 
from Sheridan, in Wyoming, to Marshall, in Minnesota, as shown by 
the following table. 
Miles from the east liix; Pressure hisht in feet 
Locality. of South Dakota. above tlie sea. 
Sheridan, Wyo 515 West . About 3,700 
Belle Fourche, S. Dak 360 " 3,030 
Pierre, S. Dak 192 " 1,854* 
Highmore. S. D 150 '• 1,928 
Miller, S. D 127 '• 1,817 
Huron, S. D 91 " 1,670 
Iroquois, S. D 71 " ' 1,638 
Marshall, Minn .33 East. 1,360 
The descent of the gradient eastward averages somewhat more than 
four feet per mile. Between Kimball and Mitchell, S. Dak., on the lat- 
itude of Chamberlain, it is ten feet per mile. 
*The pressure bights at Pierre, Harold, and some other localities, are 
too low, probably because of subterranean leakage or derivation from 
different strata. 
