628 DEPARTMENT OF TEE INTERIOR 



2 GEORGE V., A. 1912 



specially rapid attack.;}; Or, again, it is quite conceivable that a local Pliocene 

 lowland of denudation was produced in this belt of weak folding under more 

 normal climatic conditions. It is as easy to credit such an explanation for 

 these few truncated, plateati-like folds in the basalt as it is difficult to credit 

 a general peneplanation of the whole Cascade system and its later mature 

 dissection — all within the limits of the Pliocene. 



Willis and Smith both show that remnants of the Methow peneplain are 

 extremely rare and always very small within the main Cascade range where 

 they have examined it. . They speak of ' broad crests ' on a few summits which 

 are taken to be residuals. The present writer believes that practically all of 

 these can be explained as either in close organic relation to structural planes 

 like the flat roofs of batholiths, or that they can be explained by the principle 

 of the tree-line, as detailed in a following page. It may be noted that nearly 

 all of Willis's, profile sections which seem to give such a striking idea of a 

 high-level plateau are drawn longitudinally through the ridges. Transverse 

 sections would more clearly illustrate the generally deep dissection of the same 

 region. The longitudinal profile does show sympathy with the profile of the 

 canyon-cutting stream alongside the ridge ; it cannot of itself prove two erosion- 

 cycles. A set of transverse profiles would prove the general absence of high- 

 level features which can with any certainty be classed as remnants of the old 

 supposed peneplain. In other words, these latter profiles would not show 

 ' topographic shoulders,' to use another of Davis's expressive terms to indicate 

 the break in slope involved in any- such two-cycle topographic systems as that 

 here postulated by Willis, Smith, and Russell. 



The most convincing argument against the hypothesis as stated by the two 

 first mentioned authors, who ascribe the Methow peneplanation and the Entiat 

 mature dissection entirely to the Pliocene, has already been given in principle 

 in connection with Willis's hypothesis of a late Tertiary peneplanation of the 

 Pront ranges. If the extremely tough rocks of the Cascade range have been 

 baselevelled since the Miocene, should we not expect the well determined 

 Cretaceous peneplain of the Appalachian chain to have been destroyed since 

 the early (or at least middle) Tertiary upwarping of that peneplain? Or 

 should we not expect all local and even regional monadnocks like the sugar- 

 loaf residuals of New England or like the White Mountains massif of New 

 Hampshire to have been long since destroyed? No reason is apparent why 

 the Cordilleran climate has ever favoured erosion in such colossal degree more 

 than erosion has been favoured by the Appalachian climate. In many things 

 the American West claims to be more speedy and powerful than the East, but 

 such difference in the power of erosion as this cannot be conceded. And it is 

 also true that the staple rocks of the Cascades are sensibly as resistant to the 

 ; weather as those in the eastern highlands. It is true that in the states from 

 Maryland to Alabama wide belts of the Appalachian chain have been peneplained 

 in the Tertiary, but there the conditions were much more favourable to complete 

 reduction than they were in the Cordillera at the close of the Laramide revolu- 



J Cf . W. M. Davis, Journal of Geology, Vol. 13, 1905. p. 382. 



