

' YUll'Bt^l 



r ^ ^—-w^r.^ 



490 



CHANNELS OF IOWA AND WISCONSIN HILLS. 



that at Iowa and Wisconsin hills. To the east of the Wisconsin Hill school-house the crest of the 

 main ridge rises rapidly, and becomes at once covered with a heavy mass of volcanic debris ; and 

 the extent of the tunnelling has not been sufficient to either prove or disprove the existence of 

 a deep channel through here. But on the northwest side of the ridge the Morning Star tunnel, 

 driven a considerable distance into the hill, shows that as far as it has gone the surface of the bed- 

 rock here is at very nearly the same level as in the deep channel at Iowa Hill. Moreover, the 

 depth of the shaft once sunk in New York Canon, and the barometric observation at its mouth, 

 show that there also the bed-rock is very low. I think the probability strong, therefore, that the 

 old deep channel, on leaving the Iowa Hill ridge, curved slightly to the east, entering the ridge 

 on the southeast of Indian Canon at or in the vicinity of the Morning Star mine, and passing to 

 the east of the school-house, reached the head of New York Canon, and so around to Wisconsin 

 Hill. If this be correct it could only have been at a later period, when a considerable depth of 

 gravel had already accumulated in the deeper channel, that the water could have flowed over the 

 crest of the sag at Elizabeth Hill, and deposited the gravel there. When this happened, the bed- 

 rock crest of the present ridge between Elizabeth Hill and the Wisconsin Hill school-house would 

 still have remained an island in the broad gravel surface, till at last the accumulation became so 

 great as to cover even its crest. This is the most plausible theory that I can now frame for this 

 particular locality. One of the strongest objections which can be urged against this view is the 

 fact that neither at the Morning Star mine, nor anywhere else along the northwestern side of the 

 ridge between Indian and Shirt Tail canons, is there any visible proof of the present existence of 

 so great a thickness of metamorphic gravel as exists at Wisconsin Hill and around the vicinity of 

 New York Canon, as well as at Iowa Hill. The volcanic capping immediately southeast of the 

 Morning Star mine is very heavy, and the thickness of the gravel beneath it uncertain. But it 

 seems not at all unlikely that after the cessation of the flow of the main stream here, and before 

 the coming of the volcanic epoch, there may have been considerable excavation and irregular re- 

 distribution of the previously accumulated gravel by subsequent and smaller streams. 



The fact is not without interest in this connection that the top of the metamorphic gravel near 

 the Wisconsin Hill school-house, as well as at another point between there and the Morning Star 

 mine, is, in round numbers, 350 feet higher than the lowest bed-rock in the hydraulic claims at 

 Wisconsin Hill and Iowa Hill, — or 150 feet above the tops of the highest banks at Iowa Hill. 



The quantity of gravel distributed along the sides of Indian Canon for several miles above Iowa 

 Hill, the mode of its distribution, and the developments made by the tunnels at Strawberry Flat 

 and still farther northeast, point to a strong probability that Indian Canon itself occupies pretty 

 nearly the site of a branch of the ancient stream which joined the latter at a point not far from 

 where the present canon cuts it, or possibly a little farther southeast towards Wisconsin Hill. 



There seems also to have been at one time a small but well-deiined channel running southerly 

 in the spur on the east of New York Canon ; — but whether this channel had any connection with 

 Grizzly Flat is very doubtful. N 



Any further attempt to trace at present any distinct and well-marked channels in the bed-rock 

 underlying the gravel in the ridges between Shirt Tail Canon and the North Fork of the American 

 River would probably be useless. Yet the area over which the gravel is spread is very large. The 

 ridges above Iowa Hill and Wisconsin Hill, as well as between Elizabeth Hill and King's Hill, 

 have generally a heavy capping of volcanic matter, beneath which, however, there is proved by 

 the numerous tunnels to exist almost everywhere a thin layer of metamorphic auriferous gravel on 

 the rock. As a general thing this layer is but a few feet in thickness, frequently not over a foot 

 or eighteen inches, and sometimes it vanishes entirely, the volcanic matter closing clown tightly 

 upon the solid rock. Eut everywhere, without exception, wherever the surface of the rock has 

 been exposed beneath the gravel or the volcanic matter, either by hydraulic washing or by drift- 

 ing, and the rock has been hard enough to retain and distinctly exhibit the character of its original 

 surface, it has been found smoothed and worn into rounded forms by running water. 



This last remark is also true, almost without exception, wherever the ancient gravel has been 



