28o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Following the line of contact to the southeast for i mile, tlie Cambrian 

 sandstones may be seen resting directly on the massive l)eds of the Helena 

 limestone, a sli.ulit unconformity occurring at the point of contact, as shown 

 by figure 3. A mile farther to the southeast there are 6 feet of shales above 

 the limestone, a slight unconformity being shown between it and the Cam- 

 brian. The section east from Helena extends downward through some 2,000 

 feet or more of (Helena) limestone and interbedded shales and several 

 hundred feet of siliceous, greeni.sh shales before reaching the red Spokane 

 shales, which underlie the Cambrian in the Spokane Hills. 



I there found the section more comj)lete from the Spokane shales 

 (As) up to the unconformity at the base of the Cambrian Flat- 

 head quartzite (Cf), and it was in this part of the section that he 

 obtained his estimate of 2,400 feet' (731 m.) or more for the thick- 

 ness of the Helena Hmestone (Ah). It was unfortunate that 1 did 

 not make this location clear as it would probably have led Roth- 

 pletz to look there for the Helena limestone and not to assume 

 that the higher Cambrian limestones of Mount Helena were typical 

 representatives of the Helena limestone. 



C)nce having identified the Cambrian limestone of the upper j:)or- 

 tions of Mount Helena as the pre-Cambrian Helena limestone which 

 occurs far below and beneath the Empire shale in the more level slope 

 occupied by the city streets, there was little chance of Rothpletz 

 getting the true relations of the Cambrian formations and the under- 

 lying pre-Cambrian Helena limestone in the faulted and displaced 

 area south of the suburb of Lenox. 



Another confusing condition is the contact on the strike of pre- 

 Cambrian Helena limestone (Ah) and the Cambrian limestone (Cls). 

 By looking at the map (pi. 39) we find that southeast of the suburb 

 of Lenox and about 1.5 to 2 miles southeast of the thickly built up 

 south section of the city an area of Cambrian and pre-Cambrian strata 

 has been pushed to the northeast one-half mile between the fault lines 

 A-A and B-B, as shown on the map. This area includes exposures in 

 the section from the base upward of the Empire shale (Ac), Helena 

 limestone (Ah), and Marsh shales (Am) of the Algonkian, and 

 above the latter the Cambrian Flathead quartzite (Cf) and the several 

 shales and limestones (Cls) of the Cambrian before the overlying 

 Devonian limestones (Dj) are met with higher up on the hill slopes. 

 The displacement of this great mass of shales, sandstones and lime- 

 stones has brought in contact on the strike at .r (on the eastern fault 

 line (B-B) ) the pre-Cambrian Helena limestone (Ah) and the Cam- 

 brian limestones and shales (Cls) in such a manner as to cause the 

 outcrop of the Cambrian limestone to be apparently a direct con- 



^ Pre-Cambrian Fossiliferous Formations, Bull. Geol. Soc. of America, Vol. 

 10. 1899. p. 211. 



