68 HAROLD W. FAIRBANKS 



longed periods during the accumulation of the series the bottom 

 of the sea sank sufficiently rapidly to be out of the reach of lit- 

 toral sediments." 



According to the observations of the author the body of the 

 limestone is as free from detrital matter as the jasper, and 

 except for the thickly scattered calcareous remains shows 

 no more traces of organic origin than portions of the jasper. 



I cannot see that the origin through springs has anything 

 whatever to support it. It is undoubtedly true that a subsidence 

 or change in ocean currents gave rise to conditions favorable to 

 the accumulation of beds of jasper and limestone. It is, how- 

 ever, rather difficult to believe that this movement, which could 

 not have been of a catastrophic kind, should have accorded 

 exactly with the flow of hundreds, if not thousands, of springs 

 over the sea bottom, which at one period were purely siliceous, 

 and at another deposited nothing but pure carbonate of lime. If 

 the currents were as strong as the author supposes, it does not 

 seem possible that the radiolaria should have settled so thickly 

 as we frequently find them, and besides the springs possibly 

 being fresh would not form a congenial place for marine 

 organisms. 



A short discussion is given by the author to deposits which 

 he terms silica-carbonate sinter,^ the true nature of which seems 

 not to be understood. He says : "Its occurrence in extensive 

 sheets, roughly parallel with the bedding, suggests that it is a 

 contemporaneous deposit, but it may possibly be a vein forma- 

 tion. Its occurrence in the Aucella sandstones elsewhere, and 

 in the San Francisco sandstones of the peninsula is of interest 

 as a possible factor in the correlation of these formations." 

 This is a case in which wider familiarity with the Coast Ranges 

 and their mineral deposits would have readily settled a very 

 simple question. These deposits of sinter are almost always 

 associated with quicksilver ores forming Hheir gangue. The 

 quicksilver deposits are known to date from post-Miocene times, 

 and owing to their recent formation it is to be expected that 



' Am. GeoL, June 1895. 



