366 FRANCIS PARKER SHEPARD 



In Allen's section the Halysites limestone is placed in the Silu- 

 rian. This formation, however, contains the same fauna that is 

 found in the formation considered upper Richmond in the accom- 

 panying section (Fig. 2). The fauna contains the corals which are 

 generally typical of the Silurian, namely Halysites catentulatus, Fa- 

 vosites, but these are also known to occur in the west in formations 

 which are generally considered to be Ordovician,^ as for example in 

 the upper portion of the Big Horn limestone. The fauna also in- 

 cludes characteristic Upper Ordovician (Richmond) brachipods 

 among which a form of Rhynchotrema capax is most common. 

 Whether Silurian strata are actually present in the section is open to 

 question . In two localities, overlying the upper Richmond and under- 

 lying formations of Devonian age, there are several thousand feet of 

 limestone and shale in which no fossils were found. In one locality 

 the upper Richmond is overlain by a bowlder bed which strongly 

 suggests tilHte,^ and as Silurian tillites have been reported in 

 southeastern Alaska^ at a similar horizon, it is possible that this 

 formation is of the same age. 



Devonian. — The Devonian seas probably invaded the Rocky 

 Mountain trench from two directions. An invasion from the 

 south by an arm of the Jefferson seas, which covered most of the 

 Rocky Mountain region of the United States, is beheved to have 

 occupied the southern portion of the trench. Formations of this 

 age have been found by Daly at the international boundary line'' 

 and again farther north near Elko and Canal Flats by Schofield.^ 

 The fossil species collected from this formation, which are also 

 known to be present in the Jefferson limestone are Spirif er englemani 

 and S. utahensis, both of which are guide fossils for the Jefferson. 



Highly fossiliferous Devonian strata were also observed a 

 mile east of Harrogate in the Beaverfoot Range. The fauna is 

 unlike that of the Jefferson limestone, but is related to that of the 

 Devonian formations off the MacKenzie River district to the north, 



I N. H. Darton, Bull. Geol. Soc. of Am., Vol. XV, p. 399. ' 

 ^ F. P. Shepard, Jour. Geol, Vol. XXX (1922), p. 89. 



3 E. Kirk, Am. Jour. Set., fourth sec. (September, 1918), p. 511. 



4 R. A. Daly, Geol. Surv. Can. Mem. 38, p. 115. 



s S. J. Schofield, Geol. Surv. Can. Mem. 76, p. 53. 



