Fairbanks.] 



Geology of Point Sal. 



13 



water and organic matter. The residue appeared to be of an alum- 

 inous nature rather than silicious. 



Origin of the Shales. — The bituminous shales (Monterey series) 

 have already been studied by Professor Lawson.* The view was ten- 

 tatively advanced by him that the white shales were chiefly of vol- 

 canic origin. This view is based upon three considerations: (1) 

 The general poverty of silicious organisms; (2) the chemical analysis 

 corresponding rather to an acid soda rhyolite than to an organic 

 deposit; (3) angular fragments of an acid volcanic rock scattered 

 through the groundmass. The evidence seems to show that 

 the character of the silica in a part of the flints or silicious shales is 

 not an original one, but that the present chalcedonic variety has 

 been produced from the amorphous by a molecular change subse- 

 quent to deposition and solidification. The colloid or opaline 

 character of the silica at the time of deposition being recognized, 

 the question to be decided is, whether it was formed merely as a 

 chemical deposit from ocean waters holding silica in solution, with- 

 out reference to any organic origin, or whether it represents the 

 wholly or partially disintegrated silicious tests of organisms which 

 once abounded in this part of the ocean. The fact that in different 

 specimens, and sometimes in the same one, all stages of obliter- 

 ation can be noted, from those in which the structure is discern- 

 ible to those which appear as faint dots, gives support to the view 

 that the silica was derived chiefly from disintegrated organic remains. 

 The question is, as Professor Lawson admits, a very difficult 

 one. Our knowledge is too limited to say with certainty what 

 transformations sea water is capable of working out through a pro- 

 tracted interval and at a considerable depth. The bituminous shale 

 has an extensive areal development in the Coast Ranges. Its 

 greatest thickness is not known. Professor Lawson estimates it at 

 2,000 feet at Monterey. f It is probably 1,000 feet at Point Sal. 

 There are other areas in Monterey County where it is possibly 2,000 

 feet, and until the whole region is better known, any conclusion 

 reached at present is liable to need revision. 



* Bull. Dept. Geol. Univ. Cal., Vol. I, p. 26. 

 t Ibid. , p. 29. 



