NO. 4 CAMBRIAN AND PRE-CAMBRIAN AT HELENA 29I 



PALEONTOLOGICAL EVIDENCE 

 The paleontological evidence given by Rothpletz in favor of the 

 Lower Cambrian age of the " Capitol Creek shale " ( = Park shale of 

 Weed) is interesting. He tabulates it as follows:' 



Upper 

 Lower. Middle. Cambrian. 



1. Protospongia cf. fcncstrata X X 



2. Rustella edsoni var. pcntagonalis X 



3. Lingulella helena X 



4. Obolella crassa X 



5. Obolella atlantica X 



6. Acrotreta cf. sagittalis X X X 



7. Kutorgina cf. pcrrugata X 



8. Hyolifhes cf. billingsi X X 



By the above identification and interpretation of the fossils from 

 the shale a strong case is made out for the Lower Cambrian age of the 

 Park shale of Weed, or as Rothpletz states it : " We conclude that 

 the fauna of the Capitol Creek shale is doubtless Lower Cambrian, 

 but that it very possibly and indeed very probably belongs to an upper 

 horizon of the Lower Cambrian." ^ 



I wish I could agree with Rothpletz as to the Lower Cambrian age 

 of the fossils he lists and illustrates, as it would be a great pleasure to 

 me to know that the Lower Cambrian was unconformably super- 

 jacent to the Belt series of formations in this section of Montana as 

 it is on the north side of the Bow River Valley in Alberta, Canada.^ 

 Such a condition would not alter in any way the position of the 

 Helena limestone, which is far below in the pre-Cambrian Belt series. 



Stratigraphically (ante p. 281) we have seen by the section of 

 Weed at Mount Helena that the Park shale ( = Capitol Creek shale 

 of Rothpletz) is 1,100 feet (335 m.) or more above the base of the 

 Middle Cambrian and 2,455 feet (755 m.) above the base of the 

 Middle Cambrian on Beaver Creek, 20 miles (32 km.) northeast of 

 Mount Helena. This makes it difficult to consider the fauna of the 

 Park (" Capitol Creek ") shale in the Lower Cambrian even though 

 the fossils should appear to favor it. The Wolsey shale is 400 feet 

 (123 m.) below the Park shale in the Mount Helena section, the 

 interval being occupied by the Middle Cambrian Meagher limestone 

 which Rothpletz by error identified as the lower portion of the pre- 

 Cambrian Helena limestone. The fauna of the Wolsev shale zone 



^ Rothpletz, p. 41. 



^ Idem, p. 41. 



' Smithsonian Misc. Coll., Vol. 53, 1910, pp. 426-427. 



