THE FORTIETH PARALLEL SURVEY. 607 



to have been thrust upward and eastward when the flexure of the Palceozoic 

 series took place, the present dip of the Archajan schists and (|uartzites would 

 indicate that before the great Wahsatch ujjlift they were in a nearly vertical 

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



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

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

 Messrs. King and Emmons, to account for the stratigi'aphical position 

 of the rocks of the Wahsatch Range. In examining further we find 

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

 types (I., p. 107), and remarks : — 



" This classification, based upon field observations, is interestingly carried 

 out by Zirkel, whose microscopic examinations 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 absolutely no evidence whatever in favor of the belief of granitic 



extrusions later than the Archaean age As an instance of how dangerous 



any attempt 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 Archaean. They are posi- 

 tively identical down to the minutest microscopical peculiarity." (I., p. 111.) 



We now turn to the work of Professor Zirkel, whose manuscript 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 fair 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 are 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 for a considerable class of granites along the Fortieth Parallel, whose 

 petrographic constitution and habitus are identical with those of the Sierra 

 Nevada. The full details of the reasons of this assignment will be found in 

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

 memoir, 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 tlie eruptive Jurassic granites. 

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

 (VI., pp. 39, 40.) 



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



