BETWEEN INDIANA HILL AND QUAKER HILL. 



417 



The bed-rock exposures are not yet sufficient in number or extent to put to rest all doubts in 

 regard to the former position of the old channel or the mutual relations of the several channels, if 

 more than one existed. Conflicting views are still held among the miners, which it would be use- 

 less for me to attempt to harmonize. T can only record the facts as I found them to exist on the 

 ground, and leave to the future the settlement of contradictory theories. 



The bed-rock exposed to view is, for the most part, an easily cleavable slate, with a south- 

 easterly strike and a nearly vertical dip. The strike of the planes of cleavage at Indiana Hill is 

 S. 45° E. ; at the Polar Star claim, Dutch Flat, S. 35° E. ; at Waloupa, S. 28° E. ; and at Hunt's 

 Hill, S. 20° E. (all magnetic). The bed-rock, however, is not entirely uniform in character. At 

 Indiana Hill there is a portion which is less distinctly cleavable than the remainder, and con- 

 siderably harder. At the Polar Star claim much of the rock has no very distinct cleavage, but is 

 full of joints and seams. In some places masses of one variety of rock ten to fifteen feet in length 

 by two or three feet in width appear to be enclosed, like "horses" in mineral veins, within other 

 rock ; some of the rock is quite hard, while other portions are so rotten that they can be broken 

 up easily with the sledge. At Plug Ugly Hill the bed-rock is a slate, of a yellowish-brown, 

 or, in places, greenish color, soft, and rapidly weathering to a clayey mass when exposed to the 

 air. Some of the greenish rock, where weathered, shows a peculiar structure, — a structure, how- 

 ever, of which I saw a number of striking examples at the gravel mines of Plumas County. 

 For a depth of from three to eight feet the slate has become converted into a succession of 

 layers of reddish and brownish ferruginous clay, through which the vertical cleavage-planes of 

 the still undecomposed slate are frequently distinctly traceable. The clayey mass itself looks 

 as if it were regularly stratified, parallel with the inequalities of the original bed-rock surface. 

 The rock is of such a fragile character, and the clay is so soft, that it was not possible to take 



specimens. 



At the Camden claim Hunt's Hill, there are two kinds of bed-rock, one considerably harder than 



the other, though both belong to the slate series. (See specimens Nos. 174 and 175.) The plane 

 of junction between the two is nearly horizontal, the westerly dip amounting to only 10°. At one 

 point in the claim the soft rock was seen to overlie the hard variety, as shown in the diagram 

 (Plate 0, Fig. 5), the seam between them being about an inch in. thickness, and containing small 

 fragments of quartz. The whole appearance is that of a fault; but I could not satisfy myself in 

 regard to its age, whether it was older or younger than the gravel deposit. The hard rock has 

 been worn into pot-holes and fantastic shapes since the removal of the gravel, and the rate of wear 

 has been very rapid. At first sight it seemed to me impossible that so much erosion could have 

 been produced since the rock was uncovered, and I thought I had been fortunate enough to find 

 a fault of more recent age than the gravel, which might be of service in the discussion of some of 

 the doubtful points connected with the position of the old channel. Put the removal of a small 

 quantity of the soft rock, so as to bring to view a surface that the sluice waters had not acted upon, 

 showed that the original surface of the hard rock had not been water-worn, or that the evidences 

 of wear had been obliterated at the time the rocks were faulted. 



I took fresh barometric observations at or near seven of the points of which the altitudes were 

 determined in 1870, though under conditions less favorable lor accuracy than in that year. On 

 the whole I was very well pleased with the closeness of the agreement of the different determina- 

 tions, but I assign much the greater weight to those of 1870. The old and the new results for 

 these seven cases were as follows : 





1. 



2. 

 3. 

 4. 

 5. 

 6. 



7. 



Point near southwesterly end of Plug Ugly Hill . 

 Deep bed-rock in battle York mines 

 Point near site of store at Little York . 

 Empire Hill bed-rock 



Waloupa bed-rock ...... 



Bed-rock at Niece and West's old claim . 

 Point near high Hume, Sardine Flat . 



1870. 



1879.* 



Difference 



3,072 



3,090 



18 



2,70(5 



2,755 



49 



2,839 



2,8(52 



23 



2,666 



2,(59:5 



27 



2,594 



2,595 



1 



2,625 



2,613 



12 



2,911 



2,903 



8 



