VARIABLE GRADES IN THE ANCIENT CHANNEL. 281 



Tirades : 



Wherever any parts of the deepest channel between Badger hill and 

 Little York are exposed a very slight grade is almost invariably found 

 to exist; it is so at Badger hill, Grizzly hill, Hunts hill, and You Bet. 

 This is a pretty distinct hint as to the general character of the channel. 



From Badger hill to Grizzly hill, a distance of six miles, there is a 

 grade of sixteen feet to the mile. From Grizzly hill to Blue Tent across 

 the South Yuba there is practically no grade. From Blue Tent to Hunts 

 hill, a probable distance of eight miles, there is a grade of seventeen 

 feet to the mile. At Quaker hill the value found by Mr Pettee, but 

 which, according to him, is not quite reliable, was 2,650 feet, or 30 feet 

 higher than at Hunts hill. It must be remembered, however, that great 

 inequalities often exist in channels of gentle grade. In the Mayflower 

 channel, for instance, Mr Browne has shown the existence of irregulari- 

 ties of twenty feet above and below the general grade. At Scotts flat 

 the deep channel mentioned before has not been exposed. A shaft was 

 sunk long ago in the creek which did not strike bed-rock until two bun- 

 dred feet deep, at an elevation of 2,775 feet, but the channel below the 

 level of the creek is about 2,000. feet wide and the probability of strik- 

 ing the deepest depression by a single shaft without drifting is very 

 slight. 



From Hunts hill to Red Dog the channel is practically level ; neither 

 is there any appreciable difference in level betweet Red Dog and Niece 

 and West's mine at You Bet, a distance of about three miles, in which 

 the deepest channel is hidden under heavy masses of gravel* Between 

 these last-named places several drift mines have been opened up, and in 

 them, as shown by Mr. Pettee,f the deepest bed-rock is somewhat higher 

 than at either end of the channel. 



From the places there referred to as Heidliff 's and Mallory's claims 

 the bed-rock slopes down to Niece and Wests about 20 feet. Opposite 

 Niece and West's mine is an isolated fragment of the deepest channel, 

 known as " Waloupa," which place is again 30 feet lower than the bed- 

 rock at Niece and West's. This makes a total length of about one mile 

 in which the channel flowed in a nearly northeasterly direction. It is 

 certainly interesting and worthy of notice that in this rare instance of a 

 northeasterly direction the present grade of the Neocene channel should 

 liave the considerable slope of 50 feet to the mile in the opposite direction 

 to that of the river in general, so that if the present grade were also that 

 of the Neocene river it must at this point have flowed uphill for a dis- 



* Mr E. C. Uren, of Auburn; has made a spirit-level survey along the surface between tie- (wo 

 points and informs me that both have th.e same elevation, 

 t Auriferous Gravels, p. 16C. 



XLII— Bull. Geol. 8oc. Am., Vol. 4, 1892. 



