352 



University of California Publications. [Geology 



erally admitted ; in fact, a few years ago it was characterized 

 by Groth as "das Kieselsaurereichste aller Silikate, " being 

 considered a salt of pentasilicic acid, one of the five silicon 

 atoms being replaced by titanium. 



The association with contemporaneous natrolite can hardly 

 be taken as indicating the basic character of the generating 

 solutions — in fact, quite a different interpretation may be given. 

 For many years Tschermak 7 has held that natrolite is an acid 

 ortho-silicate of the formula Na 2 Al 2 Si 2 8 .H 4 Si0 4 . Doelter adopted 

 this view and presented some suggestive evidence of it 

 derived from its decomposition and synthesis, and secondary 

 origin from nepheline. 8 Recently this matter has again been 

 taken up experimentally by Tschermak 9 and Baschieri 10 , and, 

 as I believe, it has been very satisfactorily proven by the de- 

 hydration curve of the separated acid that natrolite is a salt 

 of orthosilieic acid, the formula then indicating an excess of 

 silicic acid in the solution. In regard to the basic characters 

 of the country-rock as affecting the nature of the minerals in 

 the veins, it may be noted that the polysilicate albite commonly 

 occurs in veins in the glaucophane and other basic schists of 

 the Coast ranges and in the schists themselves, associated para- 

 genetically with glaucophane, actinolite and other metasilicates. 

 Contrary to the inference drawn by Kraus, the effects of basic 

 rocks on solutions carrying Ti0 2 , if the minerals of these 

 rocks become involved in the action, should be to develop the 

 acid characters of the Ti0 2 . As a matter of observation, titanite 

 is a very common mineral in the glaucophane and associated 

 basic schists. In some of the highly siliceous veins occurring 

 in these rocks the main mass being quartz, the Ti0 2 is found 

 in the form of rutile, the basic elements not being present in 

 sufficient quantity to permit its entering into combination. It 

 does not, however, in such circumstances form a compound 

 exhibiting a basic character toward silicic acid and, as Blasdale 



7 See for example his Lehrbuch der Mineralogie (1st edition), Wien, 

 1884, and repeated in his later editions. 



s Neues Jahrbuch fiir Mineral., etc., 1890, I, p. 134. 



9 Sitzungsber. Akad. Wissensch. Wien., Math. Naturwiss. Klasse, Band 

 114, Abt. I (1905), pp. 455-466. 



10 liivista di Mm., e Crist. Hal., 36 (1908), pp. 37-48. 



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