CORRELATION OF SECTIONS 19 



limestone occurs. This series corresponds to the 5,100 feet of the Em- 

 pire, Spokane, and G-reyson strata of the Belt Mountains section above 

 the Newland limestone. Only the top beds of the latter occur at the base 

 of the Dearborn section. 



Continuing northward 120 miles Mr Bailey "Willis's section of the 

 Lewis range shows a great development of limestone at about the same 

 horizon as the Helena limestone. This, the Siyeh limestone of Willis, 

 has an estimated thickness of 4,000 feet. It is dark blue or grayish, 

 weathering buff, and contains interformational conglomerates and abun- 

 dant remains of Crj^ptozoan, a form unknown in the Cambrian and Ordo- 

 vician rocks of the Eocky mountains, but which is abundant in the lime- 

 stones of the Algonkian terranes. The presence of Cryptozoan and also 

 the stratigraphic relations described by Willis indicate that the Siyeh 

 limestone is an Algonkian formation. The series of limestones at the 

 head of Nyack creek, illustrated by plate 6, are of Cambrian or Ordo- 

 vician 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. 



The Siyeh (Helena) limestone is overlain by 1,500 feet of arenaceous 

 and siliceous beds corresponding to the arenaceous and siliceous beds 

 above the limestone of the Dearborn section. 



Subjacent to the Siyeh limestone there is 3,800 feet of highly siliceous 

 and argillaceous rocks (Grinnell and Appekunny) corresponding to the 

 5,100 feet of beds of the Empire, Spokane, and Grey son formations of 

 the Belt Mountains section. 



The siliceous beds are underlain by the Altyn limestone formation, 

 which by its contained fossils and lithologic characters is identified with 

 the Newland limestone of the Belt Mountains section. Typical fragments 

 of Bellina danai of the Newland limestone occur in the Altyn formation ; 

 also Cryptozoan. The Altyn limestone forms the base of the Lewis 

 Range section. 



The great Camp Creek, Mission Range section begins at a point 35 

 miles northwest of the Dearborn section and about 85 miles south of the 

 Lewis Range section of Willis. Its upper portions are marked by a great 

 development of arenaceous beds (la of section) above the Helena lime- 

 stone horizon of the Belt mountains and the Dearborn section. 



Below this upper grayish, arenaceous formation there is a thick belt of 

 reddish brown, arenaceous shales (1,560 feet), with more or less thin 

 bedded limestone, alternating irregularly with the greenish gray bands of 

 shales and sandstones, somewhat as in the Helena limestone series. 



This is underlain by 5,191 feet of arenaceous beds, mainly sandstones, 



