NO. 4 CAMIiklAN ASl) I'RK-CAM IJRIAN AT JIKI.KNA 2// 



Rrj'IH J'LETZ SKCTIOX OF MOUNT HELENA 



In ^reat contrast with the Mount Helena section of Weed is that 

 of Rothpletz made as a result of a brief examination in 1913/ His 

 section on the eastern slope of Mount Helena, from above downward, 

 is as follows : ''' 



6. Summit dolomite up to 230m. [ 812 ft.]. 



5. Gray schists [shales] up to 60" [ 193 " ]. 



4. Bluish-gray limestones with oolite beds 500 " [1,625 "]• 



3. Schists [shales] with limestones in alternating layers. 



2. Brownish weathering quartzitic layer. 



I. Green and gray argillaceous schists [shales]. 



Interpreting^ the above section he says, " When we compare this 

 sequence of rock with Walcott's data, it thus appears that Xo. 4 

 corresponds to his Helena limestone, which he says outcrops in the 

 upper limits of the city. Xo. 3 must then correspond to the Empire 

 shales of Walcott, and Xo. i to the Spokane* schists [shales], to 

 which Xo. 2 might be placed as the uppermost section." * 



He thinks that this interpretation can hardly be correct because 

 the schists of Xo. i have not the red color of the Spokane schists and 

 because the thick, brown quartzitic layer is peculiar neither to the 

 Empire nor the Spokane schists. He says, " A comparison for 2 

 with the Lower Cambrian Flathead quartzite would be nearer." '' 



In the above statement Rothpletz correlates Xo. 4 with the Helena 

 limestone (Ah on mapj, and it is here that the vital mistake in all of 

 his correlations was made, for his Xo. 4 limestone is the well-known 



'Bulletin 527 ("Ore deposits of the Helena Mining Region in Montana") 

 of the United States Geological Survey, with a detailed geological section 

 and map of Helena and vicinity, was available for examination in six libraries 

 in Munich in the fall of 1913. and it must have been accessible to Rothpletz on 

 his return to Munich from the United States in 1913. It was issued in Wash- 

 ington May I, 1913, and its receipt for the libraries of the Central-Bibliothek 

 des Deutschen und Oesterreichen Alpen-Vereins, Geologisch-Palaontologische 

 Sammlung des Staates, Konigl. Bayerische Akademie der Wissenschaften, 

 Konigl. Bayerisches Oberbergamt., Petrographisches Tnstitut der Universitat, 

 Zeitschrift fiir Krystallographie und Mineralogie was acknowledged by the 

 America-Institut, August 30, 1913. It was catalogued as received by the 

 Konigl. Bayerische Akademie der Wissenschaften, Math.-Physikalische Klasse, 

 1913. Heft 3, p. 76', by which institution the Rothpletz paper was published, 

 June. 1915. 



' Rothpletz, p. ID. 



^ Rothpletz evidently did not at any time see an outcrop of the Spokane 

 shale as it is exposed northeast of the railroad tracks over three miles (4.8 km.) 

 east of the city. (See As on map.; 



* Rothpletz, pp. lo-ii. 



' Idem, p. II. This is the Cambrian Flathead quartzite which is described m 

 the section of Mount Helena taken by Weed. 



