THE DIVIDE BETWEEN SLATE AND CAJNON CREEKS. 



455 



dant evidence that the old channel made frequent curvatures between La Porte and Brandy City. 

 I regret that I was unable to revisit this district and give it a more thorough examination alter my 



first hasty reconnaissance. 



Between Poverty Hill and Portwine, a distance of about three miles, there are no indications of 

 gravel on the Slate Creek slope of the ridge, with the possible exception of a small deposit at 

 Poverty Point (not shown on the map). This absence of gravel may be accounted for either by 

 supposing the old channel to have had nearly the same position as the present Slate Creek, or on 

 the hypothesis that the channel crossed from Portwine to the Canon. Creek slope, or possibly lies 

 concealed under the present lava crest. Against this latter view may be urged the narrowness of 

 the ridge for a mile or so below Portwine. It does not seem possible that a channel could be so 

 effectually concealed under this lava as to give no signs of its existence, either at its point of disap- 

 pearance or at its emergence from the lava on the opposite side. Whichever view be chosen, it 

 must be admitted that a junction of the two channels, now traceable on opposite sides of Slate 

 Creek, was effected at some point near Poverty Hill or Scales's Diggings. The Iowa shaft and 

 incline, two miles northeasterly from Scales's, and near the southeastern base of the lava-flow, were 

 sunk with the hope of finding the Portwine channel on the more easterly of the two positions 

 which it has been supposed it might have taken. It was lack of time only that prevented my 

 visitin^ these works. From all that I could learn, however, about the character of the gravel and 

 of the strata next the bed-rock, I judge that the extension of the channel has not been found. 



At Portwine there has been some hydraulic mining done at the southerly end of the gravel de- 

 posit. The extent of bed-rock uncovered is not large, but the highest bank shows a vertical face 

 of about one hundred feet. In one important respect this bank is remarkable, if not unique. It 

 furnishes evidence of the intrusion of Lava into the gravel after its deposition. (See section, Plate S, 

 Fig. 6.) The bed-rock at my point of observation pitched to the northeast at an angle of nearly 

 twenty decrees, showing that the centre of the channel was not exposed to view. The lowest bed- 

 rock accessible at the base of the bank has an altitude of 4,853 feet. Resting upon the bed-rock 

 there is a stratum about four feet in thickness of a rather coarse quartz gravel, which has been 



drifted extensively and proved to be rich in gold. Above this there is a compact rock of volcanic 

 origin three and a half or four feet thick, which the miners call "cap" rock. When freshly broken 

 the surface of this cap is bluish in color. Then there comes a stratum, ten or twelve feet in thickness, 

 of quartz gravel, neither so coarse nor so rich in gold as the one below. Above this gravel there 

 is a second cap rock, about six feet in thickness, which, upon a fresh surface, is rather light colored. 

 Above this second cap there come in succession twenty-five to thirty feet of very fine quartz gravel, 

 twenty feet of variegated pipe-clay, twenty feet of red loam, and, at top, a few feet of the common 

 volcanic surface dirt. I obtained on the spot specimens from both cap-rocks. They have been 

 examined by Mr. Wadsworth.* Both layers of cap-rock appear to come to an end towards the 

 southeastern edge of the bank, the upper one extending a little farther in that direction than the 

 lower. They are sensibly parallel to each other and conform to the pitch of the bed-rock. Were 

 it not for the fact that they come to an end within the limits of the exposed gravel, it would be 

 easy to believe that they were parts of ancient lava-flows — more ancient than the gravel. 



For a distance of two miles above Portwine, as far as Gardner's Point, there has been little or 

 no hydraulic mining done. From the prospecting tunnels and the drift diggings the general course 

 of the old channel is known to be approximately parallel to the present Slate Creek, though there 

 may be some doubt as to the precise position of the deep channel for a part of the way. This is 

 the portion of the old channel to which I paid the least attention. I got little more than a bird's- 

 eye view of the surface from high points on the Morristown trail and on the La Porte side of the 

 creek. The altitude of the bed-rock at Gardner's Point I made to be 4,845 feet. This, it will be 



* The specimen from the so-called upper cap-rock was found on examination to be a decomposed olivine-bear- 

 ing basalt. That from the lower cap-rock proved to be an undecomposed basalt, and no olivine was observed 

 in it. < 



