PHYSK AI, IIISTOUY <S0 



i.s()i;eothernis, witli what we iniiy call the plane of u;raniti(^ ru.sion, 

 had cre]it up to a position ahnornially near the surface. It is to this 

 ])rohahly that we may attribute the apparent absence of Archean rocks 

 in the (>oast ranojes, or at least the impossibility of (leHnin.<2; any rocks 

 of that period there, for these, together no doubt with great volumes of 

 later depc^sits, may be assumed to have become merged in the rising 

 granitic magma, on which strata of Triassic age are now often found 

 lying directly, arrested in the very process of absor])tion.* 



When the Tjaramide revolution occurred, by reason of the increasing 

 tangential pressure from the Pacific basin and the growing failure of re- 

 sistance of the two great geosynclines of this part of the ('ordillera, the 

 Laramide range was })roduced by the folding and fracture of a very thick 

 mass of beds, of which the crystalline base has not yet been revealed 

 b\' denudation, while in the western trough an eversion of the axis of 

 settlement seems to have occurred, resulting in the ap})earance of a 

 granitic bathylite of nearly a thousand miles in length, from which the 

 comparatively thin covering of unabsorbed beds was soon afterward 

 almost completeh^ strip])ed away by ensuing 2)rocesses of waste. 



This last great epoch of mountain making doubtless left the surface 

 of the Cordilleran belt generall}'' with a very strong and newly made 

 relief, which, before the middle of the Tertiary period, is found to have 

 become greatly modified by denudation. Chiefly because no deposits 

 referable to the Eocene or earliest Tertiary have been found in this i)art 

 of the Cordillera, it is assumed with })robability that this was a time of 

 denudation. It is further indicated that it was a time of stabilit}^ in eleva- 

 tion, by the fact that the prolonged wearing down resulted, in the interior 

 zone of the Cordillera, in the production of a great pene})lain, the base- 

 level of which shows that the area affected stood 2,000 or 8,000 feet lower 

 in relation to the sea than it now does, and that for a very long time. 

 If, however, the Puget beds of the coast are correctly referred to the 

 Eocene, it follows that the coast region was at the same period only 

 slightly lower than at present, and that the movements in subsidence 

 and elevation between this and the interior region must have been differ- 

 ential in character and very unequal in amount. 



As already noted, the earliest Tertiary sediments of the Interior plateau 

 of the Cordillera are referred to the Oligocene. Probably some further 

 subsidence at that time interrupted the long preceding time of waste. 

 This period of deposition was in turn closed by renewed disturbance'of 

 an orogenic kind, comparatively slight in amount and local, chiefly 

 affecting certain lines in a northwest and southeast direction. Next 



♦Annual Report, Geol. Surv. Can., vol. ii (N. S. ), 1886, p. 11 B et seq. . 

 XIH— Bur.r,. Gkot,. Soc. Am., Vol. 12, 1900 



