510 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



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

 of the existence of a cliif more than 5^ miles high would require to be estab- 

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

 considerable curiosity, therefore, that I paid a visit to the Cottonwood 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 beds 

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

 an old shore-L'ue, should be more or less conglomeritic ; at least, there ought to 

 be occasional zones of conglomerate, just as at the present day, we have local 

 gravel beaches on our shores. But 1 could find no trace of pebbles. It would 

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

 not mentioned by Mr. King, nor by Messrs. Hague and Emmons, and yet, as 

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

 observed them and made no reference to the fact. But not only have no peb- 

 bles of the Cottonwood granite been recorded as occurring in the overlying 

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

 approach the granite. The natural inference to be drawn from these facts, 

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

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

 centre of local metamorphism, but this change he regards as * strictly mechani- 

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

 intrusion.' How he would discriminate between a mechanical and chemical 



cause producing precisely the same idtimate 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 the uncomfortable incubus of these 

 primeval mountains. We are not required to believe in the existence of a cliff 

 5^ miles high, which maintained its position and steepness during the greater 

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

 ture of 30,000 feet on the west side of the Wahsatch Mountains." 



We see no reason for proceeding further in the examination of the 

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

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

 before us. In brief, the whole matter may be thus summed up : — 



All the crystalline and the eruptive rocks, between the Wahsatch and 

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

 ones, have been called by the geologists of this survey "Archa3an." In 

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

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

 age. In many cases the stratigraphical conditions are of a kind that 

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

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



