WORK OF BECKER, BEOWNE AND HANKS. 261 



Dr (i. F. Becker, in his paper on '^Tlie Structure of a portion of the 

 Sierra Nevada of California,"* considers the range to have existed as 

 such during the Tertiary. From the analysis of the extensive fissure 

 system discovered by him he draws the c melusion that no important 

 tilting of the Sierra has taken place at or since the post-Miocene disturb- 

 ances, but that the western slope of the range has been increased by dis- 

 tributed faults along these systems. 



For the next and very important contribution to the actual knowledge 

 of the Neocene channels one is indebted to Mr Ross E. Browne, who gave 

 the results of his careful and detailed survey of the Forest Hill divide in 

 the tenth annual report of the state mineralogist of California, 1890, 

 pages 435-465 (with maps). Mr Browne's work includes an accurate 

 topographic mapping of the contacts of the Neocene deposits and Hows 

 with the bed-rock, surveys of all tunnels and mines, and determination 

 of elevation of all important points. It is the first work of its kind, and 

 stands as a model for the many similar ones which it is hoped the future 

 will bring forth. It is gradually beginning to be recognized that de- 

 tailed surveys are indispensable when works of such magnitude and 

 cost are contemplated as the opening of important gravel channels. 

 Both on the Forest Hill and Placerville divides large sums of money have 

 been lost by neglecting a sufficiently extended topographic and geologic 

 survey of the region in question. 



To Mr Browne belongs the credit of having first distinctly recognized 

 the different systems of later channels (channels of tire volcanic period) 

 as contrasted with the older pre-volcanic drainage system. In ( Jood year's 

 notes from Forest Hill and Placerville the existence of such channels 

 is, however, plainly implied. Mr Browne also gives a diagram showing 

 the grades of the Neocene rivers with reference to the longitudinal axis 

 of the Sierra with the view of ascertaining whether tilting of the range 

 can be recognized in the grades of the Neocene channels. f He thinks 

 more data are needed, but " that the evidence, as far as it goes, is against 

 any considerable increase in the slope of the Sierra flank — decidedly 

 against an increase large enough to account per se for the two thousand 

 feet deeper cutting of the modern river." In the same report Mr John 

 Hobson has carefully described and mapped the Iowa, Hill divide in a 

 similar detailed way.J 



Mr Henry G. Hanks§ still appears to maintain a glacial or partly 

 glacial origin of the gravels. I fear that in upholding this theory he is 

 contending against very heavy odds. No evidence whatever of the ex- 



* Bull. Geol. Soe. Am., vol. 2, pp. <>1 and 7:;. 



fOp. eit,, p. 445. 



| Op. eit., p. 419. 



I Mining and Scientific Press, San Francisco, April 5, 1890, and following numbers. 



