APPENDIX—GEOLOGICAL SURVEY. 
421 
it comes out at the spring it is between the lower beds of the 
blue limestone and but a very few feet above the sandstone, 
giving at least a vertical depth of 250 feet. Unless this sink 
hole extends through the whole of these strata, we cannot 
conceive how water in a turbid state could possibly find its 
way in so short a time to such a depth ; especially when we 
consider that the lower beds of galena limestone and the up¬ 
per beds of the blue (strata equally favorable for the escape of 
water) crop out above the spring along the side of the same 
hill. 
There are many other sink holes in this elevation of consid¬ 
erable interest, especially those at the West Blue Mounds. 
Approaching the mounds from the west, these sink holes seem 
to converge as though they would center in this elevation. 
Ascending the mound from the west side, we find, about half 
way from the base to the summit, two or three sink holes near 
each other; one of them of considerable depth showing a 
ledge of rock for at least twenty-five feet. On the north side and 
nearer the summit, instead of sink holes we find slight de¬ 
pressions with a damp, marshy surface, while on the east side, 
near the summit, and full four hundred feet above the sur¬ 
rounding country we find several never-failing springs of water. 
The West Blue Mound is 1,150 feet above Lake Michigan, 
or nearly 1,800 feet above the sea, and is one of the highest, if 
not the highest point of land in the state of Wisconsin. To 
suppose that this large marsh on the north side near the sum¬ 
mit from which are cut several tons of hay every year, and 
those springs on the east side, a little higher up are supplied 
with water from what falls on the summit of the mound, is 
absurd. To account for the water that supplies these springs 
and this marsh land at this altitude but two other ways are 
left us. One of these is hydrostatic pressure, the other is me¬ 
chanical force acting from below. 
If a body of water can be found at this altitude or above 
it, with a possible connection with these springs, then this 
body of water will be, in all probability, the source. But if 
such a body of water cannot be found, then our only chance 
