THE CHANNELS: IN PLACER COUNTY. 



105 



surfaces, the little furrows and ridges produced by weathering being often from half an inch to an 

 inch deep, and running horizontally across the nearly vertical faces of the columns. Many of the 

 columnar surfaces are, however, not corrugated ; and some of them are as smooth as if polished ; 

 the external crust, in such cases, having its texture entirely changed to a, depth varying from an 

 eighth of an inch to three quarters of an inch in thickness. This change of texture, which on the 

 whole seems most likely to have been produced simply by the chemical action of water, is one 

 from the ordinary, sharp, granular condition of volcanic ash, to a peculiar compact, and almost 

 opaline, or semi-vitreous state, The rock of this bluff is quite hard, rings sharply in large pieces 

 under the hammer, dresses, splits, and chisels easily and well, and is said, probably with truth, to 

 furnish the best quality of building-stone of any locality near Placerville. 



The whole crest of the main ridge near and above the " Twelve Mile House," on the Carson 

 road from Placerville, is made up of volcanic debris, and the thickness of this material must be, 

 in places, at least, fully 700 or 800 feet. 



Negro Hill, northeast of Placerville, is capped with "black lava" or volcanic breccia, which 

 throughout the hill is generally very hard. The same material extends over all the highest por- 

 tions of Cedar and Hangtown hills south of the town. 



The crest of the main ridge between Jackson and Sutter Creek is capped with volcanic gravel. 

 The same material frequently caps other ridges in this section of the country, and often lias beneath 

 it a little metamorphic gravel, which here and there has been worked to some extent by drifting. 



6. The Channels: their Width. 



It is impossible to define with accuracy the width of the deep channel at Iowa Hill, since the 

 hydraulic workings, extensive as they an;, do not uncover the rims, and high bed-rock is known to 

 exist at one or two points so located as to render it more than probable that the width is far from 

 uniform. This difficulty is further increased by the great depth of the channel, which appears 

 from the barometric observations to be about 200 feet in the bed-rock. But it is evident that at 

 the northwest end of Wiessler's ground the channel was at least from 400 to GOO fcet wide, while in 

 the central portion of the ridge the strip of ground still standing beneath the town of Iowa Hill is 

 so narrow, and the extent of the pits already worked on either side is so great as to render it ex- 

 tremely probable that the width of the deeper portion of the channel in its narrowest part is not 

 less than 200 feet. 



In the Lebanon Tunnel, on the northeast side of Now York Canon, they have followed a well- 

 defined channel in the bed-rock which generally ranges from sixty to eighty feet wide, although 



in places much narrower ; it curves somewhat, but its general course is southerly, and it has a 

 decided descending grade in that direction. 



At the Tunliel of the Eclipse Company, in Grizzly Canon, the channel is about 300 feet wide, 

 and some fifty or sixty feet deep. 



At the Mountain Gate Tunnel, near Damascus, where the channel has been followed for 4,000 

 feet, it has been found to bo from 175 to 200 feet in width, and the rise of the rock towards either 

 side, so far as they have been worked, is very genii e, the extreme points reached at the sides being 

 not generally eighteen or twenty feet higher than the central and lower portions of the channel. At 

 the Cement Mill Tunnel, near Damascus, the channel lias been worked out to an average width of 



nearly one hundred feet. The bed-rock rises considerably higher on each side of the channel. 



In Yule's Claim, at Startown, the channel is very wide, but not deep. At Nick Anderson's 

 Claim, just below Last Chance, near Startown, the average width of the outer channel is from 

 seventy-five to one hundred feet ; that of the back channel is about 300 feet. 



At the Reed Mine, near Dcadwood, the width of tlie channel is said to be sixty or eighty feet, 

 ftnd the Basin Channel at the Devil's Basin, where the trail from Dcadwood to Last Chance begins 

 to descend into the canon of the North Fork of the Middle Fork of the American River, about 

 eighty feet. This is the width actually worked in the Basin Channel and rich in gold; but the 







