290 W. LINDGREN — TWO NEOCENE RIVERS OF CALIFORNIA. 



slight southward slope from the Morningstar works to Wisconsin hill. 

 Mr Hobson's arguments, based on the occurrence of serpentine bowlders 



in certain parts of the channel and on the relative elevation of the rhyo- 

 litic strata, are stronger. There are, however, such difficulties involved 

 in carrying the principal channel in the direction advocated by Mr 

 Hobson that I cannot adopt his view as the most probable. 



Bath to Ralstons. — In discussing the upward continuation of the 

 large and deep channel at Bath, which is the same as that of the May- 

 flower mine. Goodyear indicated several reasons why it was probable 

 that it came down from the Long canyon country, the principal ones 

 being the occurrence in it of granite bowlders and its capping of" white 

 lava' 1 (rhyolite). The vicinity of Long canyon was only examined in a 

 cursory way by < roodyear. There is. indeed, at the Ralston mine, in the 

 western part of the divide north of Long canyon, unmistakable evidence 

 of an outlet of a large and important channel; there is, further, a re- 

 markable and striking similarity between the accumulations of the Ral- 

 ston channel with those of the Bath-Mayflower stream : there is, further, 

 no other way open for the Ralston channel than in the direction of Bath, 

 for higher bed-rock bars the way both to the south and to the north ; 

 hence I feel justified in concluding that a connection once existed be- 

 tween the two channels, which has since been eroded by the recent 

 stream of the Middle fork. 



Mr Browne is struck with the considerable extent to which the modern 

 rivers on the Forest hill divide have avoided the older channels, leaving 

 them buried under the volcanic flows on the top of the ridges.* To ex- 

 plain it he assumes that the ancient valley was tilled with volcanic ma- 

 terial only up to its widespread rims, but not to overflowing, and that 

 the modern rivers started by preference along the marginal lines of the 

 deposits. A study of the geologic map of the country north and 

 south of the Forest hill divide will show that there is no good reason 

 for such an assumption. On the contrary, the last flows almost com- 

 pletely flooded and buried the Neocene valley and its divides in this 

 vicinity : the only points rising above them were the high hills to the 

 west of the " Brimstone plains " and the Volcanoville hill to the south- 

 ward. Only on the upper part of the Georgetown divide were there any 

 continuous and important bed-rock ridges projecting above the general 

 level of the flows. 



The explanation of Mr Browne might well he applied to certain parts 

 of the upper river courses, hut I do not think it explains the positions of 

 the present streams on the Forest hill divide. .Slight inequalities in the 

 surface of the andesitic flows probably determined first the directions. 



♦ Tenth Ann. Rep. of State Mineralogist of California, p. 44-j. 



