50 The American Geologist. July, 1894 
100 horse-power, and in quantity enough to flood a twenty-acre field six 
inches deep in twenty-four hours. Many pages arc occupied with simi- 
lar details, indicating a simply enormous supply of artesian water in 
South Dakota at a depth less than 1, (KM) feet. The water is found in the 
Dakota sandstone, which outcrops along the eastern Hanks of the Black 
Hills. The supply therefore enters the stratum along thai outcrop, and 
doubtless also on the western border of 1 he plains. Analysis shows that 
it is a permanently hard water, as might be expected, containing in a 
gallon fourteen grains of sulphate of lime, four grains of carbonate of 
lime, and the grains of magnesic carbonate. 
In the third paper. Prof. Hay says that the same Dakota sandstone is 
the water-bearing formation in the Arkansas valley, and that it obtains 
some reinforcement from the underlying Jurassic strata. Doth crop 
out around the Black Hills and in the upper Missouri riverregion. The\ 
allow water to pass through them very freely, as is shown by the Ciant 
Spring described by Lewis and Clark eighty years ago and still flowing 
as in their day, witli an estimated yield of one hundred cubic feet a 
second or nearly 50,000 gallons a minute. 
The great water-bearing stratum of large portions of the plains is a 
Miocene gril of an exceedingly absorbent nature, underlying extensive 
lacustrine beds of marly sill. At least half of the rainfall, or five inches 
yearly, is estimated by Prof. Hay to sink into the ground and to be held 
chiefly in this grit, from which it flows forth in copious springs along 
the river banks, wherever these have been cut down low enough to ex- 
pose the grit. Water is also found in wells when sunk to its level, at 
the depth of from 50 to 300 feet below the general surface. Prof. Hay 
points out that these artesian waters are not derived from the moun- 
tains for the most part, because that source of supply is almost, entirely 
cut off by the outcrop of the water-bearing stratum before if reaches 
the mountains. 
The importance of the water problem is forcibly stated by Prof. Hill 
in the fourth part of this volume, where he says: 
•'In the western half of the United States the water question is not' 
only serious but paramount to every other consideration, for there are 
vasl areas, as large as all New England, such as the great Llano Esta- 
cado, without a single brooklet, river, or permanent pond upon the sur- 
face: while there are other areas, aggregating one tenth of the Union, 
which together do not possess a stream of the volume of the Connecti- 
cut or Mohawk, and are utterly lacking in the accompaniments of fre- 
quent laterals and springs. Greal railway lines — the Southern Pacific 
for example — are obliged to haul water hundreds of miles for their en- 
gines, and have spent millions in not always judicious experiments to 
obtain an underground supply. - ' 
The Llano Estacado is described as one of the most remarkable geo- 
logical features of the continent, — an area of 50,000 square miles, lying 
more than one thousand feet above the sea, and surrounded with a pre- 
cipitous rampart which is gashed here and there by river valleys cut 
out of the nearly level strata of late Miocene or Pliocene date. No water 
