REVIEW AND GENERAL DISCUSSION. 



197 







(though rare) small pebbles. It never forms the matrix of volcanic breccia, conglomerate, or 

 gravel \ that matrix being always a darker-colored material of altogether different texture and 

 appearance. Where the white lava is in heavy masses it often shows a tendency to columnar 

 forms, and at a few localities, mentioned in the preceding notes, well developed prismatic columns 

 may be seen. There is a striking analogy in physical character and appearance between some 

 varieties of the white lava and the material of the volcanic table-land north of the head of 

 Owen's Valley, though it would probably not be difficult in any case to distinguish the one 



from the other. 



The presence of the granite boulders in the banks at Bath would seem to furnish additional 

 evidence also, pointing to the same direction for the course of the stream which brought them. 

 For everywhere excepting at Bath, in the country where I travelled to the north of the Middle 

 Fork of the Middle Fork, granite is extremely rare among the boulders either of the metamorphic 

 gravels or of the volcanic accumulations ; and by far the nearest point to Bath where granite bed- 

 rock exists higher up in the mountains is in the Long Canon country, or between Long Canon and 



the South Fork of the Middle Fork, and granite boulders are common throughout the Long 



Canon country. 



Moreover, if it be true, as Mr. Kates believes, that a ridge of very high bed-rock stretches from 

 Volcano Canon near Baker's ranch entirely across the ridge to Shirt Tail, this would seem to 

 imply of necessity that the How of the great channel at Forest Hill could not have proceeded for 

 any great distance above that town from the northeast, in spite of the fact that at Forest Hill its 

 course appears to have been southwest. 



I think therefore, the evidence is very strong that at some time during the gravel period a large 

 stream once flowed in the general course that I have indicated above. And yet, the shifting char- 

 acter, even of the largest streams engaged in piling up the gravel, must not be forgotten. 



Mr. Pond's estimate of the ground that has been hydraulicked off at Todd's Valley, and the 

 amount of gold obtained from it,* would give, in round numbers, about 8,000,000 cubic yards 

 washed away, with an average yield of about fifty cents per cubic yard for the whole. This yield 

 per cubic yard would correspond tolerably well with the yield from the ground washed by Mr. 

 Pond within the last few years, as already given. 



I think it not at all improbable that the great channel at Forest Hill may be continuous under 

 the central portion of the ridge, passing a little northwest of Todd's Valley, to a point as far south- 

 west as Peckham Hill. But at or near Peckham Hill, if not before, it must pass out of the ridge ; 

 and below (that is, southwest of) there the country is so low that neither gravel nor volcanic 

 matter remains upon the present hills. 



There is little doubt, I think, that a great field yet remains for mining enterprise in this Forest 

 Hill ridge. But one great drawback there now is lack of water for hydraulic and other purposes. 

 Furthermore the " back channel " there can never be worked to advantage without the previous 

 expenditure of large sums of money in the driving of new tunnels, etc. 



The general character of the upper basin of the Middle Fork of the American, immediately 

 before the modern canons began to be excavated, appears to have been that of a broad smooth 

 plain, with a gentle southwesterly slope, just about equal in amount to the average southwestern 

 slope of the Sierra Nevada, while at the same time the surface of the basin probably sloped very 

 gently inwards from the edges in all directions towards its central portions. The surface of the 

 country here at that time seems also to have consisted chiefly of volcanic matter in the form of 

 ashes, breccias, and conglomerates or gravels which had slowly accumulated to depths varying from 

 one or two hundred to 600 or 800 feet over the buried auriferous gravel. Here and there isolated 

 patches of bed-rock might have been seen at the surface, the accumulation of volcanic matter, 

 great as it was, being insufficient probably to entirely bury all the older hills, which, however, 

 seem to have very rarely projected much, if any, above the general level of the volcanic surface. 



Through this plain the canons of the modern branches of the Middle Fork have been slowly 



* See ante, p. 118. 



