42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



than those of the Brisco but both indicate somewhat similar conditions 

 of sedimentation. We did not find any physical evidence of a systemic 

 break at the upper limit of the Beaverfoot formation. Beneath the 

 Beaverfoot the Wonah Ouartzite of the Sinclair Canyon section is 

 formed of a clean wave-washed beach sand more or less cross-bedded 

 and varying in thickness in relative short distances. Subjacent to the 

 quartzite the shales and sandstones of the Sinclair formation of the 

 lower Ordovician were found to be over 1,600 feet (487.7 m.) in 

 thickness, and beneath them occur the limestones and shales of the 

 Ozarkian Mons formation, more than 3,800 feet (1,158.2 m.) thick. 

 Ai; Sabine Mountain 34 miles (54.7 km.) south of Sinclair Canyon 

 the Beaverfoot is superjacent to the lower portion of the Mons. The 

 Wonah Ouartzite Sinclair formation and over 3,000 feet (914-4 ^■) 

 of .the Mons are absent, presumably from nondeposition. 



On returning from the field I looked up the occurrence of the 

 Richmond horizon to the south in northern Utah and found that the 

 Fish Haven Dolomite with a Richmond fauna is superjacent to the 

 Swan Peak Ouartzite, which in turn rests on the Garden City lime- 

 stone containing a lower Ordovician (Beekmantown) fauna and 

 beneath the latter the St. Charles formation with a lower Ozarkian 

 (Mons) fauna. 



I found that the evidence from the Cordilleran area is in favor of 

 including the Beaverfoot with its Richmond fauna in the Silurian, and 

 the same seems to be true from the diastrophic or physical view wher- 

 ever a formation carrying the Richmond fauna is superjacent to an 

 Ordovician or pre-Ordovician formation. 



The evidence of the faunas has been well presented by Dr. E. O. 

 Ulrich ' who holds that the break between the Richmond fauna and 

 that of the Maysville of the Cincinnatian is probably greater than that 

 at the summit of the Richmond. 



With the physical (diastrophic) record in the Cordilleran Province 

 and the character of the " Richmond " fauna on which to form a 

 conclusion, the Beaverfoot formation of this paper is placed in the 

 Silurian. This is based on the presence of a great disconformity and 

 unconformity at the base of formations carrying a Richmond fauna 

 that is wide-spread on the North American Continent, and the change 

 in the fauna between the Maysville fauna of the Cincinnatian (Ordo- 

 vician) and the basal fauna of the Silurian (Richmond). 



^The Ordovician-Silurian Boundary. Congres Geol. Int. Compte-Rendu de la 

 XII" Session Toronto 1913, pp. 593-667. 



