372 FRANCIS PARKER SHEPARD 



is only 15 miles to the south in the Fort Steele region, and appears 

 to be traceable this far north. The clastic nature of the deposits 

 as against the limey deposits of the Upper Cambrian (and perhaps 

 Middle Cambrian) indicates that there was variation in the charac- 

 ter of the sedimentation in the Cambrian. In the vicinity of 

 Parsons the Upper Cambrian is somewhat argillaceous, but the 

 base of the Ordivician is mostly limestone. 



If the Beltian is actually present at the base of the "clastic 

 series," it seems as though the greatest change during the Beltian 

 and Cambrian times was a change from semiterrestrial and near 

 shore deposits to deposits in clear broad seas. Probably this 

 change is of more importance than any minor unconformities that 

 may exist below the lowest rocks which are known to contain 

 fossils. 



CORRELATION OF UNFOSSILIFEROUS FORMATIONS 



Correlation of the unfossiliferous formations over wide areas by 

 lithological comparison has been resorted to frequently in the 

 Cordillera. Dawson, McConnell, and others who made the 

 pioneer surveys of the region relied especially on this method. 

 Daly, as has been shown above, also correlated formations of 

 widely separated portions on the same basis. Mistakes made in 

 one of these attempts is illustrated by the recent findings concern- 

 ing the Purcell series (p. 369). 



The most detailed work on the unfossiliferous formations is 

 that by Schofield in the Cranbrook area. Here the members of 

 the Purcell series are mapped over an area of about 2,500 square 

 miles. The characteristics of the different formations are such 

 that they are Hkely to vary considerably, and to grade from one into 

 another rather readily, so that with the great complication of the 

 fault system in the region, a classification is extremely difficult. 



From observations based chiefly on the fossihferous formations, 

 it appears that classification of the unfossihferous formations is 

 especially complicated by the extreme variability of the lithology, 

 and of the metamorphic character of the formations along the 

 trench. 



Lithological variations. — The lithological character of the differ- 

 ent horizons in the Paleozoic was examined at several places along 



