STRATIGRAPHY ALONG THE ROCKY MOUNTAIN TRENCH 371 



below is marked. (3) Basal conglomerates of the Cambrian have 

 rounded fragments of the underlying argillites. 



This evidence does not necessarily place the underlying Siyeh 

 formation in the pre- Cambrian. That the Olenellus horizon is not 

 nearly at the base of the Cambrian is shown by the great thickness 

 of Lower Cambrian below the Olenellus horizon in the Waucobian 

 of California. Whether the length of the time bridged in this 

 disconformity is sufficient to place the underlying formations 

 in the Beltian, is open to doubt for the following reasons: (i) The 

 degree of metamorphism varies greatly in members of the same 

 age in the Purcell series. (2) The difference in the thickness of 

 the Siyeh formation is not important, because of its clastic nature. 



(3) The occurrence of the conglomerate does not prove an uncon- 

 formity, as conglomerates are common in the "clastic series." 



(4) Since there are great abundance and all varieties of argillites in 

 the "clastic series" the fragments of argillites in the Cambrian 

 conglomerates may have come from argillites other than those 

 directly underlying the conglomerate. In general it may be said 

 that minor unconformities are to be expected in a series of this 

 sort, and their significance is not great. Since the contact of the 

 Cambrian on the pre-Cambrian has been especially well studied, 

 it is not surprising that minor unconformities should be found at 

 some horizon not far below the lowest horizon that is known to be 

 fossiliferous. 



From observations on the relation of the "clastic series" to 

 the "limestone series" farther north in the trench, new but rather 

 incomplete evidence was found of the relation between the older 

 series and the Upper Cambrian limestones (the base of these lime- 

 stones may be Middle Cambrian). At Premier Lake, below what 

 are probably the Upper Cambrian limestones, there is a series of 

 argillaceous quartzites and shales. While no accurate measure- 

 ment of the series was made, it was estimaetd to be at least 5,000 

 feet thick. As the series was examined in several places and 

 was found to be quite similar in character in all of them, the condi- 

 tion of sedimentation is thought not to have varied in any important 

 degree. This series is probably, at least in part, of the same age as 

 the Purcell and Galton series farther south. The Purcell series 



