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THE rOUTIETH PARALLEL SUllVEY. 



507 



to have been thrust upward and eastward when tlie flexure of tlie ralooozoic 

 series took phice, the present dip of the Archoian schists and quartzites would 

 indicate that before the great AYahsatch uplift they were in a nearly vertical 

 position, flanked to the east by the granite mass." 



Wc may now investigate a little more in detail the question of the 

 nature and origin of the granite, as well as the thcorieB put forth by 

 Messrs. King and Emoions, to aecount for the sti'atigraphical position 

 of the rooks of the Wahsatch Uangc. In examining further we find 

 that Mr. King divides the eruptive granites of his survey into four 

 types (L, p. 107), and remarks: 



" This classification, bused u]ion Held ol)servati(nis, is interestingly carried 

 out by Zirkel, whose microscopic cxaniinatious in every way confirm the field 

 arrangement." (I., p. 109.) 



Of these types the Wahsatch granite is taken as the youngest ; but 



he says : 



** There is absolutelv no evidence vv^hatever in favor of the belief of granitic 



extrusions later than the ArcluTjan age As aii. instance of Jiow dangerous 



any attemj)t to correlate age by petrological features alone really is, may be 

 cited the Jurassic granite of California and the granite, of the Cottonwood 

 region on the Wahsatch, which is unmistakably Arch;ean. They are posi- 

 tively identical down to the minutest microacopi('.al peculiarity." (L, p. 111.) 



We now turn to the work of Professor Zirkel, whose manusoript was 

 revised by Mr. King and his assistants previous to its publication. And 

 since all his information in regard to the field relations of the rocks was 

 obtained from them, we may assume that his statements give a fltir idea 

 of Mr. King's views at the time of its publication. He remarks : — 



" The decidedly eruptive granites may be divided into two classes : one em- 

 braces those older rocks that arc of ante-Jurassic age ; the other, those which 

 have obtruded themselves through the Jurassic strata. For the enormous 

 mass of eruptive granite of the Sierra Nevada, Professor "Whitney has demon- 

 strated a Jurassic origin; and, although not definitely proven, a similar age is 

 assumed i'or a considerable (dass of granites along the Fortieth Parallel, whose 

 petrographic constitution and habitus are i<lentical with those of the Sierra 

 Nevada. The full details of the reasons of this assiu'nment will be found in 



the chapter upon granites in Vol. I. of this series. When, therefore, in this 



menxtir, Jurassic granite is spoken of, the intention is to designate that family 



of which the Sierra Nevada occurrence is the type in age and constitution. 

 . . . . Clarence King has long since shown that the eruptive Jurnssic granites, 



and only these, are characterized by the presence of macroscopical titanite. " 



(VT., pp. 39, 40.) 



It has been seen that Mr. King divided the eruptive granites into 



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