PROBLEMS IN STRATIGRAPHY ALONG THE ROCKY 

 MOUNTAIN TRENCH 



FRANCIS PARKER SHEPARD 



University of Chicago 



In an investigation of the structure of the Rocky Mountain 

 trench, from Gateway, Montana, to Golden, British Columbia,^ 

 the writer came in contact with some of the stratigraphic problems 

 of the Canadian Cordillera. For determination of fossils and for 

 helpful criticism he wishes to acknowledge his indebtedness to 

 Dr. Stuart Weller. 



STRATIGRAPHIC SERIES ALONG THE ROCKY MOUNTAIN TRENCH 



From the fossils collected at various localities and the sections 

 which have been previously made of the trench, it was possible 

 to map with some degree of accuracy a large part of the zones 

 flanking this great vaUey (Fig. i). There are two principal 

 series of rocks represented. One of these is dominantly clastic, 

 the other dominantly limestone. The former contains many meta- 

 morphic varieties of shales, sandstones, and conglomerates, but 

 the metamorphism is not extreme. Limestone is not lacking in the 

 clastic series, but most of it is in thin bands. (For convenience 

 this series will be termed the "clastic series.") 



The age of these formations is somewhat problematic. In those 

 places where it has been studied hitherto, it has been generally 

 considered pre-Cambrian, but fossils found recently in one locality 

 have shown part of it at least to be as young as Lower Cambrian.^ 

 That the series is older than Upper Cambrian is indicated by the 

 following points: (i) In a number of places it was found underlying 

 Upper Cambrian formations, and nowhere has it been observed over- 

 lying formations containing Paleozoic fossils. (2) It is in general 

 metamorphosed more than formations of the limestone series. 



' F. P. Shepard, Jour. GeoL, Vol. XXX (1922), p. 130. 

 ^S. J. Schofield, Science, Vol. LIV (1921), p. 666. 



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