REVIEW AND GENERAL DISCUSSION. 



489 







at various points, but chiefly along the southeastern side near Indian Canon, and in the shallow 

 patch which caps the ridge near the Catholic church a little northeast of Iowa Hill. The total 

 quantity already washed away is probably between two and three million yards, of which I esti- 

 mate nine tenths to have come from the deep channel at Iowa Hill, and the balance from smaller 

 pits at other points. This would leave between twenty-three and twenty-four million cubic yards 

 yet capable of being hydraulicked. How much of this it will ever pay to wash, is a difficult ques- 

 tion to answer. But probably the greater portion of it will do so whenever the supply of water 

 shall be plentiful, reliable, and cheap. 



Such estimates as these must be taken only for what they are worth. In this case I esti- 

 mated the area by pacing, and had the barometric determinations of the maximum heights of the 

 banks to guide me, together with such information respecting the lay of the bed-rock under the 

 gravel as my other explorations, and the statements of men who have worked here in shafts and 

 tunnels, gave. 



The deep channel at Iowa Hill is perfectly well defined, crossing the crest of the ridge in a direc- 



■ 



tion a little to the east of south. It is very rare in the country through which I have travelled to 

 find an ancient channel cut so deeply into the bed-rock as this,- — the rims on either side being 

 fully 200 feet above the bed of the channel. The width of the. latter across the top from rim to 

 rim, at Iowa Hill, appears to be something over 2,000 feet, and may be half a mile, — the exact 

 locality of the highest part of the southwestern rim being somewhat uncertain. 



The barometric observations will show that the bottom of this channel at Iowa Hill is consider- 

 ably lower than the bed-rock at Indiana Hill and Gold Run on the opposite side of the river. 



I think there can be little doubt that Dutch Flat, Gold Run, Indiana Hill, Iowa Hill, Wisconsin 

 Hill, and some points in the Forest Hill divide mark the ancient course of a river which corre- 

 sponded in the gravel period to the present North Fork of the American. 



Though the ancient stream appears to have crossed the present one between Indiana Hill 

 and Iowa Hill, yet there is a striking approach to parallelism between the general course of the 

 modern stream and that of the ancient one as thus indicated from Dutch Flat to the Forest Hill 

 divide; and if, as is more than probable, the ancient stream, on reaching the latter point, curved 

 rapidly again to the west of south, this parallelism becomes more striking still. 



This is the only instance I have seen in which the course of so large a stream at the commence- 

 ment of the gravel period can be traced with so much approximation to certainty for so many 

 miles. It is probable also that throughout the greater portion, if not the whole, of the gravel 

 period, this stream, between Dutch Flat and the point where its course is intersected by the present 

 Shirt Tail Canon, was subject to far less change and shifting of its bed than was generally the case 

 with the streams elsewhere. The depth to which this channel was excavated in the solid rock, 

 and the correspondingly great and uncommon depth of the auriferous md amorphic gravel which 

 has been accumulated between such narrow limits along its course, all speak strongly in favor of 

 comparative permanence in the course of this stream through a very long period of time. 



But, prominent as the general outlines of this stream appear to be, and clearly as it seems to be 

 defined at some localities, yet, even in this case, when we attempt to trace its course in detail from 

 one locality to another, we encounter many difficulties. From Iowa Hill to Wisconsin Hill, for 

 example, though, these tw r o places arc so near together, the exact course which w r as followed by the 

 stream is somewhat doubtful. According to the barometric observations, it would appear that 

 while the lowest bed-rock in the claims at Wisconsin Hill is a little lower than it is at Iowa Hill, 

 yet at Elizabeth Hill it is some forty or fifty feet higher than it is at Iowa Hill ; while all the way 

 along the crest of the ridge from Elizabeth Hill towards the east as far as the Wisconsin Hill school- 

 house the bed-rock is higher still. It appears, therefore, that while the stream was running in its 

 lowest bed, it could not have passed through Elizabeth Hill, nor anywhere through the present 

 ridge between there and the Wisconsin Hill school-house ; nor is it probable that it passed to the 

 west of Elizabeth Hill. Yet the depth of the metamorphic gravel on the crest of the sag at Eliza- 

 beth Hill is very considerable, and it is perfectly similar in its general appearance and character to 





