300 The American. Geolog hi. May, i89o 
considerable depths some other tlian tlie usual causes of arte- 
sian flow must be looked for. We think that there is a cause 
ready to our hand suflticient for all such phenomena. It is 
,alvvays in operation and might 1je expected sometimes to pro- 
duce such results. 
This cause we will call rocli ^pressure. All rocks in the 
earth's crust contain some water. The more 23orous rocks 
contain the greater quantity. At a distance below the surface 
the superincumbent strata sul^ject the rock masses to enor- 
mous pressure. If we assume that the rocks of Kansas to a 
depth of one thousand feet have an average specific gravity 
three times as great as that of water we are probably within 
bounds, as, though limestones and sandstones are usually 
somewhat less, the presence of iron in many of the beds will 
bring up the average considerably. On this basis a prism of 
the rocks to the depth of 600 feet and one inch square would 
Aveigh 781 pounds, which is equivalent to a pressure of 52 
atmospheres. If, then, 25 feet be taken as the measure of a 
column of these mineralized waters equivalent to one atmos- 
phere, the rock pressure would be more than the equivalent 
of a column of water twice this hight. 
Let a water-bearing stratum at a depth of 600 feet as at 
Richfield, be pierced by the drill we should then have the 
rock pressure of 52 atmospheres squeezing the water out of the 
rock pores and, granting sufficient plasticity in the rock and 
a sufficient quantity of water, it must rise in the tube which 
has only the pressure of one atmosphere ujion it. A large 
bore to the well and a small supply of water would be against 
its reaching the surface. On the other hand a bed rock with 
mobile molecules at or near saturation, under this enormous 
pressure must cause in a narrow tube a flowing well. At 300 
feet the rock pressure would be only half that given above or 
26 atmospheres and the column of water to be supported will 
be diminished in proportion. At other depths the same pro- 
portions will hold good. 
Here then we have a force that may be merely an aid in 
some cases of artesian flow which is mainly due to the usual 
causes of such flow, and which is a most efficient cause for 
the constant flow of wells whose depth is great and whose 
(juantity of water is small. We are inclined to consider rocl:- 
pressurc as the cause of the flow of the Pottawotamie and 
