184 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



which is less than 15 miles distant from the Nyack creek locality. It is 

 difficult to avoid the suspicion that these Castle Mountain limestones are, in 

 truth, identical with the Siyeh limestone, in which, therefore, Middle Cambrian 

 fossils may at some future time be discovered. Walcott has, however, come to 

 a quite different view. He writes : 



' The series of limestones at the head of ISTyack creek, illustrated by 

 plate 6, are of Cambrian or Ordovician age, as indicated by fragments 

 of fossils that I found in them. I do not think the Siyeh limestone is to 

 be correlated with them, nor with the Castle Mountain limestones of 

 McConnelL't 



Walcott's latest correlation paper for this region contains a section on the 

 Dearborn river, which carries both Middle and Lower Cambrian fossils. ff The 

 fossiliferous rocks are quite conformable and show a thickness of 2,205 feet; 

 they are chiefly massive or thin-bedded limestones (described as weathering 

 jellow to buff at some horizons), with interbedded shales. The description of 

 the rocks is of essentially the same quality as that which must be applied to 

 the Siyeh formation. Only a few miles away another section of somewhat 

 similar beds, with, however, dominant argillites, had been measured by Walcott, 

 and the whole referred to the Algonkian as part of the ' Belt terrane.'* No 

 statement is given as to the precise relation of these two sections except the 

 following (page 203 of the 1908 paper) : 



' Beneath the Cambrian sandstone the Empire shales of the Belt 



Terrane of the Algonkian occur with apparently the same strike and dip 



as the base of the sandstone. Traced on the strike, however, they appear to 



be unconformably beneath the sandstone.' 



If the apparent unconformity should be explained in the manner suggested 

 (on a later page) by the present writer, it follows from these studies at Dear- 

 born river that the Empire shale is either Lower Cambrian or is not signifi- 

 cantly older than the Lower Cambrian. In favour of the writer's view is the 

 fact that these Dearborn river sections occur at points more than 100 miles 

 distant from the old shore-line zone of the Belt mountains, that is, at such a 

 part of the geosynclinal downwarp where the Lower Cambrian beds should be 

 expected to appear in fairly full development. 



We have, therefore, at ISTyack creek, Belton, and the Dearborn river, three 

 localities where fossiliferous Cambrian formations lie, respectively, side by 

 side with typical members of the ' Belt terrane.' At one or more of these points 

 some geologist may be fortunate enough to find the paleontological evidence 

 which will, at no distant day, fix the position of the Belt terrane among the- 

 standard geological systems.f 



JBull. Geol. Soc. America, Vol. 17, 1906, p. 19, 



ft C. D. Walcott, Smithsonian Miscellaneous Collections, Vol. 53, 1908, p. 200. 



*C. D. Walcott, Bull. Geol. Soc. America, Vol. 17, 1906, p. 8. 



t In this connection it is of interest to note that, as reported by Wood in 1892, "in 

 the vicinity of Missoula, a few fossils were obtained in the silicious limestone (dolo- 

 mite) and identified by Mr. Charles Schuchert as Obolella." The relation of this for- 

 mation to the Belt terrane is not stated. Herbert Wood, Amer. Jour., Sci., 3rd ser.,. 

 Vol. 44, 1892, p. 404. 



