172 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



possible that several thousand feet of still younger rocks were piled upon the 

 Lone Star formation. Assuming the present normal temperature gradient of 

 about 1° C. per 100 feet of descent, the Monk and Irene formations must have 

 had original temperatures ranging from 150° to 300° or more Centigrade. 



It is evident that rock-shearing and the formation of new, metamorphic 

 minerals under the tremendous tangential stresses of mountain building, were 

 greatly facilitated by these relatively high degrees of heating. One can hardly 

 wonder that every member of the' Monk formation and almost every foot of the 

 Irene formations, show some schistosity. In the Monk formation the increase of 

 shearing with depth of original burial is well shown in the conglomeratic bands, 

 ~b, d, h and /. The conglomerate of members b and d is identical in appearance 

 with the conglomerate bands of the overlying, relatively unsheared Dewdney 

 formation. On the other hand, the pebbles of members h and j show strong 

 pressure-flattening or stretching, like that characterizing tne basal Irene 

 conglomerate. 



Analogous relations were observed in the Purcell series. While the Moyie, 

 Kitchener, and upper part of the Creston quartzite seldom showed schistosity 

 even when strongly deformed, the lowest beds of the Creston often displayed 

 a tendency toward the development of sericitic schists where deformed to about 

 the same extent. This parallel behaviour of the Summit and Purcell series under 

 similar dynamic stress favours, though of course not compelling, the correla- 

 tion of the two series as parts of one huge sedimentary prism. 



In general, it may be stated that, from the summit of the Selkirks to the 

 Great Plains. on the Forty-ninth Parallel, the sediments of the Rocky Mountain 

 Geosynclinal to a depth of about 20,000 feet below the top of the Carboniferous 

 limestone, show few traces of what is ordinarily called dynamic metamorphism. 

 This does not mean that the strata have not been strongly upturned, for at 

 many points they approach or reach verticality. Within that 20,000-foot zone 

 the sediments have been thoroughly indurated and very largely recrystallized, 

 but almost entirely through static metamorphism (Belastungsmetamorphismus) ; 

 the recrystallization seems to have been essentially completed before the prism 

 was folded and faulted. Below the 20,000-foot zone the rocks were at such 

 temperatures and pressures that, when deformation began, shearing and true 

 dynamic metamorphism with the creation of schistose structures, were the rule. 



SPECIFIC GRAVITY OF THE GEOSYNCLINAL PRISM. 



During the laboratory study of the rock collections, specific gravity deter- 

 minations of the stratified rocks were often found to be desirable. The pur- 

 poses of the determinations were so various and the number of specimens 

 handled so considerable that it involved but little extra time and labour to make 

 a fairly complete set of determinations for the typical, fresh specimens col- 

 lected between Waterton lake and the summit of the Selkirk range. The result 

 has been to give a tolerable idea of the average specific gravity of the different 

 formations composing each series. 



