610 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



crystalline rocks have once more been revealed by dcuudation. Now the fact 

 of the existence of a clilf niore than 5-J niilus high vvoidd re(j_uire to be estab- 

 lished by very carefully collected and convincing evidence. It was with very 

 considerable curiosity, thei'efore, that I paid a visit to the Cott(niwo(jd district, 

 where the evidence was said to be most complete. I must frankly own that I 

 failed to observe any grounds on which the assertion appeared to me to be 

 warranted. One would naturally expect that if a mass of strata 30,000 feet 

 thick had been laid down against a steep slope of land, its component l)ed3 

 ought to be full of fragments of that land. Each marginal belt, representing 

 an old shoredine, should be more or less conglomeritic ; at least, there ought to 

 be occasional /.ones of conglomerate, just as at the present day, we have local 

 gravel beaches on our shores. But I couhl lind no trace of p(;bhles. It would 

 of course be presumptuous in me to assert that they do not exist ; but they are 

 not mentioned by Mr. King, nor l)y Messrs. Hague and EnnuonSj and yet, as 

 their evidence woukl be so important, we can hardly suppose that these writers 

 observed them and made no reference to the fact. But n(^t only have no peb- 

 bles of the Cottonwood granite been recorded as occuning in the overlyiug 

 Paleozoic rocks, it is admitted that these rocks become metamorphosed as they 

 ap])roach the granite. The natural inference to be drawn frtjui these facts, 

 one might suppose, would be tliat the granite is later in date than tlie rocks 

 overlying it. Mr. King admits that the granite has been undoubtedly the 

 centre of local metamorphism, but this change lu^ regards as ' strictly mechani- 

 cal and not to be mistaken for the caustic phenomena of chemically energetic 

 intrusion.' How he w^ould discrinvinate l>et\ve(m a mechanical and chenucal 

 cause pr*)ducing precisely the same ultimate effect he does not explain 



"But if I am correct in regarding the Wahsatch granite as of post-Carbon- 

 iferous date, then we are relieved from tlic nncomfoifable incubus of these 

 primeval mountains. AVe are not re([uired to believe in the existence of a clilf 

 5J miles high, which maintahied its position and steepness during the greater 

 part of all geologicnl time. And we are spared the necessity of a colossal frac- 

 ture of 30,000 feet on the west side (jf the Wahsatch Mountains.' 



Wc sec no reason for i)rocccding further in the examination of the 

 work of the Fortieth Parallel Survey. Enough has been said to give a 

 sufficient idea of its character and value, as bearing on the question 

 before us. In brief, the whole matter nmy bo thus sunimed up : — 



All the crystalline and the eruptive ro(;ks, between the Wahsaf ch and 

 the borders of California, with the exception of the modern volcanic 

 ones, have been called by the geologists of this survey "Arcluean." In 

 not a single instance, so far as we are able to make out, has there been 

 positive proof given that the rocks thus assigned were really of that 

 age. In many cases the stratigrapliical conditions arc of a kind that 

 such proof could not possibly have been obtained. In order to main- 

 tain the view of the Arehican age of the rocks in question in certain 



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