184 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
The prominent point just north of Nevada City, known as the Sugar Loaf 
(as already mentioned), is 3,111 feet above the sea level, and 670 feet above 
the bed of Deer Creek at the Suspension Bridge. The extension westerly 
of the voleanic ridge, on which the Sugar Loaf forms a partly isolated and 
therefore rather conspicuous mass, is called Cement Ridge. Its general 
direction just beyond the gap which separates the portions of the ridge, is 
S. 21° W. (magnetic), but a mile or so farther on it becomes more nearly 
west. Cement Hill is a few feet lower than the Sugar Loaf, directly opposite 
which it seems to form almost a flat table of lava, sloping off gradually to- 
ward the west. Dean’s Tunnel is on the northwest quarter of Section 1 (T. 9 
E.; R. 16 N.), about two miles northwest of the centre of Nevada City. The 
course of this tunnel is a little west of south, and it is run in a much decom- 
posed syenitic granite, resembling the usual bed-rock in this vicinity. This 
granite has undergone decomposition in a very irregular manner; so that, on 
the line of the tunnel, there are still “ boulders,” — as the undecomposed por- 
tions of the rock are called, — which cannot be removed by the use of pick 
and shovel, as the rest of the material can be. This tunnel had been driven 
400 feet at the time when visited by us; but another one, forty-three feet 
higher up, had been carried in for a distance of 900 feet on the bed-rock, 
before striking the gravel. This higher tunnel was not low enough to strike 
the channel, but was run 575 feet in the gravel without having got entirely 
across it. The question of the connection of the channel here with that of 
the mines east of the Sugar Loaf, known as the Manzanita Diggings, is one 
of very considerable difficulty. The following extract from Professor Pettee’s 
notes gives the results to which he was led by his examinations in this 
re@ion : — 
In exploring the Cement Hill Ridge, in the direction of Peck’s Diggings, nothing but volcanic 
was seen until I began to descend the spur between Long Tom and Native American ravines ; 
and here, about 700 or 800 feet south of Peck’s house, the end of the lava was reached, this alti- 
tude being about 2,700 feet. The measurement of the lower edge of lava on Cement Hill, oppo- 
site the Sugar Loaf, had given me as a result 2,835 feet. Peck’s house is on the unsurveyed land, 
but he said the corner stake between sections 2, 3 (and what would have been and will be when 
sectionized), 34 and 35, was between a quarter and half a mile pretty nearly due south of his 
house. Long Tom Ravine is on the east, and Native American Ravine on the west of Peck’s; 
into the last-named of which his old diggings, which are mostly open excavations, discharge. He 
selected a spot.for me which was nearly an average bed-rock, and the barometer indicated an alti- 
tude of 2,632 feet, which is only about twenty feet lower than the bed-rock in the Manzanita 
Diggings. A difference so small as this was unexpected (though there were some who declared 
that the bed-rock at Peck’s was even higher than at the Manzanita Diggings), and I am sorry that 
arrangements were not made to have a short series of synchronous observations at the two places, 
extending over three or four hours. The distance between the two places is not far from three 
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