186 DEPARTMENT OF THE INTERIOR 



2 GEORGE V.„ A. 1912 



to expect that the lower part of such a colossal deposit would show more 

 induration than the upper part. 



Microscopic examination of many specimens has, in fact, showed that in 

 each of the Forty-ninth Parallel series, static metamorphism has operated much 

 more strongly in the older formations than in the younger, quite conformable 

 ones. This rule is, however, not absolute. Many of the Grinnell beds still 

 largely preserve their original clastic structure, while the overlying argillaceous 

 beds of the Siyeh are now typical metargillite. In the field these Grinnell strata 

 look as young as the Carboniferous shales in the mountains farther north. 



The writer was much struck with the relatively slight induration of the 

 sandstones at the base of the Moyie and Gateway formations. Yet there can 

 be little doubt- that they are, respectively, thoroughly conformable to the 

 Kitchener and Siyeh formations and, with these, make a mass of continuous 

 sedimentation. These particular sandstones tire just those which the writer 

 has, on other grounds, correlated with the Flathead sandstone. In all these 

 cases the relative lack of metamorphism is to be attributed more to the peculiar 

 nature of the sandstone than to any great difference of age between each sand- 

 stone lens and the immediately underlying beds. 



It appears fair to conclude that the criterion of relative induration does 

 not imply a great erosion-gap between the Belt terrane and the Middle Cambrian 

 sandstone. 



Evidence of Unconformity. — The one controlling principle used in referring 

 the Belt terrane to the pre-Cambrian consists in postulating a strong uncon- 

 formity between the Middle Cambrian Flathead sandstone and the entire series 

 below the top of the Marsh shale, the uppermost member of the terrane at the 

 original localities. The unconformity is believed by Walcott and his colleagues 

 to be similar to that found between the Middle Cambrian Tonto sandstone and 

 the tilted Chuar series in the Grand canyon of the Colorado. In his original 

 announcement of the westward extension of the unconformity beyond the 

 region where Peale had first suspected its existence, Walcott wrote as follows: — 



' The unconformity now known proves that in late Algonkian time 

 an orographic movement raised the indurated sediments of the Belt terrane 

 above sealevel, that folding of the Belt rocks formed ridges of considerable 

 elevation, and that areal (sic) erosion and the Cambrian sea cut away 

 in places from 3,000 to 4,000 feet of the upper formations of the Belt 

 terrane before the sands that now form the middle Cambrian sandstones 

 were deposited.'* 



In one of his later publications Walcott states that : — 



' One hundred miles farther north the section appears to be conformablo 

 from the Ordovician down through the Middle Cambrian and the Lower 

 Cambrian of the Bow River series, and not to reach down to the Algonkian 



*€. D Walcott, Bull. Oeol. Soc. America, Vol. 10, 1899, p. 213. 



