370 /. C. BRANNER 



Sierras, in California, are replacements of clays by silica, 1 and 

 that others are possibly replacements of limestone by silica. 



Wadsworth came to believe in their sedimentary origin. 2 



Rutley in a review of the subject reached the conclusion that 

 the novaculites were replacements by silica of dolomites or of 

 dolomitic limestones. 3 



Hinde expressed the opinion on the occasion of the reading 

 of Rutley's paper that these rocks were of organic origin. 4 



Lawson thinks the "radiolarian cherts," that is, the jaspers 

 of the coast ranges of California, are local deposits chemically 

 precipitated from submarine siliceous springs. 5 



Branner thinks the jaspers are of organic origin. 6 



Van Hise in speaking of certain jaspers of the Marquette 

 district says : " It appears highly probable that dynamic action 

 transformed the ferruginous chert into the jasper." 7 



Derby's views, that novaculites are replacements of lime- 

 stones by silica, are given in the first part of the present paper. 



Fairbanks has concluded that the Tertiary siliceous shales 

 of the coast ranges of California are derived from diatomaceous 

 beds. 8 



Doubtless many other expressions of views regarding the 

 origin of these siliceous rocks might readily be found, but these 

 are enough to show that there has been the widest possible 

 difference of opinions on the subject. 



We have then the following theories, that the novaculites, 

 jaspilites, jaspers, etc., are : 

 i. Mechanical silts. 

 2. Organic silts. 



'Bull. Geol. Soc. Am., Vol. Ill, pp. 421-422, 440, 1892. 



2 M. E. Wadsworth, Rep. State Geol. for 1891-2. State Board of Geol. 

 Surv. (of Michigan) for 1891-2. Lansing, 1893, PP- 75 -I 55> dated March 1892. 



3 Quart. Jour. Geol. Soc, Vol. L, p. 386, 1894. 



4 Quart. Jour. Geol. Soc, Vol. L, p. 391-392, 1894. 

 515th Ann. Rep. U. S. G. S., pp. 425-426, 1895. 



6 Trans. Amer. Soc. C. E., Vol. XXXIX, p. 58. Read Nov. 17, 1897. 

 JMonog. U. S. G. S., Vol. XX VIII, p. 372, 1897. 

 8 San Luis Obispo folio, U. S. G. S. (MSS.). 



