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IOWA ACADEMY OP SCIENCES. 
onyx deposit here may be, we could not determine, but there 
are some reasons for believing the material to be abundant. 
Its geological history, at present, is not altogether clear, but 
it may be assumed that all such limestone formations have 
been formed in caves. The cave or caves where this was 
formed must have been near by, for the fragments are of such 
shape as to show but little abrasion from ice or water. The 
cave seems to have been crushed by the glacier, crowded up 
against the side of the mountain and left there without any 
further disturbance. It seems probable that the scene of the 
action of the glacier must have been mainly lower down 
towards the foot of the mountain, otherwise this soft onyx 
would have been reduced to limestone mud. It also seems 
very probable that caves, in which this onyx forms or grows, 
no longer exist in this region, unless it might be a short dis- 
tance to the west from the present mine, where heavy deposits 
of calcium carbonate exist and where such deposits are now 
forming. Where this supply of material, necessary to form 
the onyx and soft, limy hills, near by, was obtained, we did 
not discover, but there must be limestone in the mountain not 
far away. 
At the extreme western end of this long valley, which is 
about one-half mile long, and a few rods west of Soda creek, is 
a tine spring of moderately cool water, supersaturated with 
carbon dioxide. This spring is in the midst of a flat area of 
several acres, much of which shows plainly that springs once 
existed almost everywhere over it, and now, only a dozen rods 
away, are large springs yielding an abundance of hydrogen 
sulphide, the odor of which may frequently be detected a quar- 
ter of a mile distant. The “soda spring,” as it is called, 
referred to above, issues now through a round hole about one 
foot in diameter, in a heavy block of sandstone. The spring is 
covered by a neat pavilion, ten or twelve feet square, with 
comfortable seats around the inside. It is a general resort for 
campers at the springs. The carbon dioxide comes up in 
great bubbles and the water is delightfully acid There is no 
evidence at this spring that the water carries any limestone 
with it. Along the banks of the Bear, near by (this spring is 
probably ten to fifteen rods from the river), were thin, soft, 
shelving rocks, of what are supposed to be calcium carbonate, 
four or five feet in total thickness. On the south side of the 
river were rounded hills twenty feet or more in height and of 
