

392 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 



discoveries been made, which would tend to throw light on any doubtful point. It will not oe 

 necessary for me to go afresh over the ground covered by Mr. Hague, Mr. Bowie, and others, 

 whose reports have appeared in printed form, and my notes will relate principally to points of 

 detail and to some questions in regard to which there is room for a difference of opinion. 



On page 200 of this volume it is stated that the bed-rock between San Juan and Cherokee is 

 slate. This is partly true, without doubt, for the bed-rock at Badger Hill is distinctly a slate ; and 

 it is probable that the high hill or ridge, which lies to the west, and which caused the old channel 

 to turn towards the north near Cherokee, is also of slate ; but it is certain that the granite which 

 forms the bed-rock at San Juan and at Montezuma Hill extends, along the line of road from the 

 Oak Tree Ranch to Cherokee, to within a few rods of the town. I did not attempt to trace the 

 line of junction between granite and slate, but as there is a granite country -rock on the opposite 

 side of the river, a little below Camptonville, I am inclined to think that the most of the rock for 

 three or four miles above San Juan is also of that character. Above Cherokee the rock exposed is 

 all slate as far as Bloomfield, with the exception of some of the rock at Malakolf. 



The bed-rock exposed at the Malakolf mine is mostly a metamorphic slate, varying considerably 

 in character within short distances. . It is sometimes quite hard and again it is comparatively soft. 

 According to Mr. Hamilton Smith, who had an excellent opportunity to become acquainted with 

 this rock while the long tunnel was in process of construction, it frequently contains seams or belts 

 of bluish quartz, which may be regarded as due to some local siliciheation or to some intrusion of 

 foreign matter. There are no regular slips nor cleavage seams. A so-called granite belt, forty or 

 fifty feet in width, cuts across the slate bed-rock in a zig-zag course. It is exposed to view in the 

 mine, near shaft No. 8, and has been struck in the deep tunnel and at points on the rim. There 

 is a sharp line of demarcation between the slate and the granite.* 



That the old channel between San Juan and Badger Hill has been washed away admits of no 

 doubt ; there is no other path for it save that now occupied by the canon -of the Middle Yuba. 

 The difference of level between the bed-rock at San Juan and that at Badger Hill I make to be 

 358 feet. The distance between the points in a straight line is four miles, which, allowing for 

 windings, corresponds to a grade of about eighty feet to the mile. The position of the deep bed- 

 rock is nowhere known between Badger Hill and the Malakolf mine, near Bloomfield. The 

 bed-rock exposed at Grizzly Hill lies off the line of the main channel. The altitude of the bed-rock 

 at Malakoff, shaft No. 8, I make to be 2,929 feet, or 538 feet above that at Badger Hill. The 

 distance along the supposed course of the old channel is seven and a half miles. The grade, 

 accordingly, was seventy-two feet to the mile. 



As just stated above, the precise course of the old stream between Badger Hill and Malakoff is 

 not known,^ but we may be sure that it followed approximately the line of gravel as laid down on 

 the map. ^ The only question about which there can be any serious doubt is as to the relation of 

 the deposit at Grizzly Hill to the rest of the mass of gravel. On page 201 of this volume, in the 

 quotation from Mr.^ Hague's report, a branch or tributary is spoken of as " coming from the south- 

 east (Grizzly Hill)," and on page 202 there is an allusion to the slight inclination of the bed-rock 

 between Badger Hill and Grizzly Hill. The difference of level between these points I cannot 

 give as accurately as I would like to, hut all the measurements agree in making this differ- 

 ence less than one hundred feet. The distance between the points is six miles. According to my 

 barometric measurements the bed-rock at Grizzly Hill is ninety-three feet above that at Badger 

 Hill, but the data obtained from Mr. McMurray, to which reference will again be made further on, 

 make the difference only fifty-five feet. Again, my barometric measurements show that the 

 Grizzly Hill bed-rock is only 445 feet below a given point at Malakoff, while the surveys of Mr. 



* 

 ■ 



* The specimen which was taken from a point scarcely five feet distant from that from which the slate speci- 

 men was taken, was examined microscopically by Mr. Wadsworth, who designated it as an -altered andesite,"- 

 perhaps equivalent to " propylite (?) . " It was difficult to get satisfactory specimens of this rock. There had 

 evidently been pretty extensive surface changes through the action of water, even during the short time that the 

 rock has been uncovered. 



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