REPORT OF THE CHIEF ASTRONOMER 171 



SESSIONAL PAPER No. 25a 



For example, the Moyie-Gateway sandstone sub-prism thins rapidly east- 

 ward and does not appear at all in the Clarke and Lewis ranges, its place being 

 taken by the contemporaneous Sheppard magnesian quartzite and the red rocks 

 of the Kintla. The thick magnesian limestone of the middle Siyeh thins toward 

 the westward, being dovetailed first into argillite and then, farther westward, 

 into sandstone, both of which rocks are contemporaneous with the limestone. 

 The limestone in its most westerly outcrops occurs in the form of several thin 

 tongues running out westward from the main limestone sub-prism into the 

 Kitchener quartzite. The sub-prisms of red beds have already been described. 

 The thick sub-prism of silicious and magnesian limestone composing the Altyn 

 thins out somewhere between the Yahk river and the Wigwam river, being 

 replaced on the westward by the contemporaneous Creston quartzite. The 

 great lenses of Dewdney conglomerate and Wolf grit similarly, but more 

 rapidly, thin out to the eastward and are replaced by homogeneous Creston 

 quartzite. 



The lithological variations in the geosynclinal as a whole, when considered 

 in transverse section, are relatively, rapid, distances of only fifty or a hundred 

 miles corresponding to profound differences of composition in contemporaneous 

 strata. Tbe persistence of the lithological units along the NW.-S.E. axis of 

 the geosynclinal seem to be much more pronounced than in the transverse 

 section established on the Boundary line. Yet the work of McConnell and 

 Dawson north of the line and of several American geologists, particularly 

 Walcott, Willis, Lindgren, Bansome, Calkins, and MacDonald, all working in 

 Idaho and Montana, shows that, even along the Cordilleran axis, there is con- 

 siderable lithological variation among contemporaneous beds of the geosyn- 

 clinal. 



The maps and sections accompanying this report represent the outcrop 

 and relations of lithological individuals. If sufficient paleontological evidence 

 to date the strata of all the series in an actual time-scale ever be secured, and 

 the same Boundary belt be mapped to show the outcrops of strictly contempo- 

 raneous formations, that map would have a very different look from the one 

 here presented. 



METAMORPHISM OF THE GEOSYNCLINAL PRISM. 



One of the most notable features of the Monk formation (Sum- 

 mit series) as it crops out in the Monk creek section, is the pro- 

 nounced increase of metamorphic effects over those witnessed in the 

 overlying and similarly upturned sediments. Slaty cleavage and true 

 schistosity are inconspicuous structures in the Wolf, Ripple, and Beehive 

 formations but are regularly recurring structures at most horizons of the Monk, 

 Irene Volcanic, and Irene conglomerate formations. The development of these 

 secondary structures on so great a scale is doubtless related to the original 

 depths of burial of the lowest three members of the Summit series. Before 

 the series was flexed up, the beds of the Monk formation lay blanketed beneath 

 at least 15,000 to 20,000 feet of the overlying conformable beds; it is very 



