96 IOWA ACADEMY OF SCIENCES. 



onyx deposit here may be, we could not determine, but there 

 are some reasons for believing the material to be abundant. 

 Its geoloo:ical 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 fine 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 



