448 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 
bed-rock. He also told me that in the neighborhood of the main mass Sheets of lava, from one 
foot to four or five feet in thickness, and lying in nearly horizontal positions, were found penetrat- 
ing the gravel beds for as much as fifty feet, and that in many cases blocks of detached gravel 
were completely encased in lava. The only explanation consistent with the observed facts is 
that after the deposition of the gravel, it was broken through forcibly by an eruption from below. 
Other interesting facts of a similar nature will be given on a subsequent page. 
The eastern rim-rock at La Porte also shows signs of having been disturbed, so much so that in 
some places it actually overhangs the gravel. During the period of the removal of the gravel this 
abnormal position of bed-rock was very noticeable. I have the authority of Mr. Hendel for saying 
that the layers of gravel and sand could easily be seen to conform to the displaced position of the 
rock. The section (Plate 8, Fig. 3) was taken from one of Mr. Hendel’s old note-books, having 
been made by him when the curvatures could be distinctly seen in the mines. 
The disturbance of the eastern rim is further illustrated in the prospecting tunnel upon which 
Mr. Ellis was at work at the time of my visit. Mr. Ellis holds some peculiar theoretical views as 
to the origin of the gravel deposits, and has commenced a tunnel in the eastern rim-rock in the 
hope of proving their correctness. The tunnel is 115 feet long. It starts in the broken rock 
which has fallen from above, but the rock soon gets harder, and for fifty feet is of a dark color, 
with the exception of one light-colored clayey seam. Fifty feet from the mouth of the tunnel 
there is to be seen a narrow strip of rolled gravel in the roof; and twenty-five feet farther in 
there is again gravel in the roof, and bed-rock also above the gravel. The slates above the tunnel 
are nearly horizontal, instead of having a dip of from 65° to 70° to the east as they do a short dis- 
tance away. Everything points to the conclusion that the overhanging bed-rock in its fall has 
caught and enclosed occasional bunches of gravel. 
It seems probable also that the position of the Spanish Flat gravel has some relation to these 
disturbances. Spanish Flat lies just to the southeast of the main La Porte deposit, but its bed- 
rock is about one hundred and fifty feet lower than that at the outlet of the La Porte mines. 
Upon the sloping surface of slate rock between the two places I saw quartz gravel at almost every 
step. The dip of the bed-rock, particularly on the northwestern side of the Flat, is very irregular, 
changing within a few feet from the vertical to forty-five degrees on either side, and being in 
places nearly horizontal. The rock in the central portions of the Flat is more nearly normal in 
appearance. The gravel, particularly in the upper twenty feet, shows the same “sand-drift” 
arrangement which is so noticeable in the upper layers of the La Porte gravel. This deposit sug- 
gests many interesting inquiries, for which no easy answers are ready. May it not be possible, for 
instance, that the La Porte channel, either before or after the deposition of the main mass of 
gravel, occupied this lower level? Or, may it not be possible that a connection once existed by way 
of the Claybank gravel with some channel now concealed under the lava to the northeast? The 
Claybank deposit lies about a quarter of a mile to the east of the central portions of the La Porte 
mines, and its bed-rock is said to be 160 feet lower than that at La Porte. See Mr. Hendel’s 
section (Plate S, Fig. 5). I could not make any satisfactory examination of this deposit. There 
has been no bank exposed by hydraulic washing, and it did not seem worth while to try to pene- 
trate the old tunnels, in which no work has recently been done. It is probable that they are inac- 
cessible. The ground is said to have been prospected by a tunnel 2,400 feet in length “ nearly all 
through gravel, with 1,250 feet of cross or side drifts to the right and left, all in gravel.” The 
current reports are that good rolled gravel was found, and that the pitch of the bed-rock was such 
as to lead to a belief in the existence of a deep channel under Bald Mountain. It is indeed sup- 
posed by some persons that the Claybank deposit is the natural southwestern outlet of the Gibson- 
ville channel. If this supposition be true, some very difficult questions will arise in regard to the 
mutual relations of the two channels, which here so nearly approached each other, and yet flowed 
at such different levels. The question, From what direction did the old channel come? is one of 
practical importance to the owners of mining property in the vicinity of La Porte. To this ques- 
tion I will not attempt to give a final answer. In the time at my disposal I could not become 
