262 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



a few fragments of fossils from the Meagher Hmestone and Park 

 shale of the Cambrian, my objective being largely to discover the 

 relations existing between the basal formation of the Cambrian 

 [Flathead quartzite] and the pre-Cambrian formations. The Helena 

 limestone was examined north, west, and east of Mount Helena and 

 its thickness was roughly measured on the line of my diagrammatic 

 section southeast of the suburb of Lenox. 



WALCOTT DIAGRAMMATIC SECTION OF 1899' 

 The diagrammatic section showing the relations between the Cam- 

 brian and Belt terranes, to which Rothpletz refers a number of times, 

 began on the east with the section of the Belt Mountains in the 

 vicinity of White's Canyon, thence passing over the Lake Beds of the 

 Missouri River Valley to the eastern base of Spokane Hills, north 

 of the boundary line between Lewis and Clark and Jefferson counties. 

 Passing over the Spokane Hills, it next extends across the Lake 

 Beds of the broad Prickly Pear Creek Valley about a mile and a 

 half (2.4 km.) north of the boundary line between Lewis and Clark 

 and Jefferson counties, and a little north of East Helena, where it 

 bends to the west-southwest, near its crossing of the Northern Pacific 

 and Great Northern Railway tracks ; this was in order to avoid 

 striking into the fault line (B-B) about a mile east of Lenox. South- 

 west of the railway tracks the section passes over an area underlain 

 by the Empire shale (Ae),'' and reaches the Helena limestone (Ah) 

 in the foothills about 1.25 miles (2 km.) southeast of the suburb of 

 Lenox, or about 2 miles (3.2 km.) from the thickly settled suburb 

 in the southeastern portion of the city of Helena. In the diagram- 

 matic section (fig. 10) the Helena limestone is represented as being 

 overlain by formations that include Cambrian, Devonian, and Car- 

 boniferous strata. No attempt is made to represent the character of 

 the Cambrian in the sketch other than by a strong black line and lines 

 above it, since the point desired to be brought out in the section and 

 the text was the thinning out of the Helena limestone (Ah) and Em- 

 pire shale (Ae) both from the east and west toward the Spokane 

 Hills, and that a great unconformity was indicated by the fact that 

 the Cambrian rested on the Spokane shales in the Spokane Hills with 

 the Helena limestone and Empire shale absent, and that in the Belt 

 Mountains as well as in the vicinity of Helena both of those forma- 

 tions were present between the Spokane shales and the Cambrian. 



^ Bull. Geol. Soc. America, Vol. 10, p. 211. 



^The lettering used is the same as that on the map (pi. 39). 



