NO. 4 CAMBRIAN AND PRE-CAMBRIAN AT HELENA 275 



generally small, but occasionally attaining a diameter of one inch. 

 Because of the lithologic character and stratigraphic relations of the 

 sandstone, it is correlated with the Flathead quartzite of the Little 

 Belt Mountains section. 



" Immediately above the Flathead quartzite is a mass of soft strata 

 about 750 feet thick. Continuous exposures of this portion of the 

 stratigraphic section do not occur, but wherever observed the rocks 

 consist mainly of fissile micaceous shale, prevailingly of a greenish 

 hue. There are occasional intercalations of platy, calcareous layers, 

 containing numerous greenish granules, presumably of glauconite. 

 Three collections of fossils were obtained from these rocks in the 

 vicinity of Half Moon Pass. The lowest fossiliferous zone occurs 

 very near the base of the formation and from this zone Asaphiscus 

 capclla Walcott, Hyolithcs sp., and Ptychoparia sp. were obtained. 

 About 170 feet higher stratigraphically fossils identified as Obolus 

 matinalis (Hall) were found in abundance in a calcareous layer. 

 Still higher, fossils determined as Asaphiscus capclla Walcott were 

 collected ^ 



" Overlying the Wolsey shale is a formation with very distinct 

 and characteristic lithology. It is composed of layers of firmly 

 cemented, flat, limestone pebbles, with thin parting of gray fissile 

 shale. The thickest layer of conglomerate noted was 4^ feet, and 

 the general average was 2 or 3 feet. Worm trails and ripple marks 

 are plentiful on the upper surfaces of the conglomerate layers, so it 

 would appear that the formation represents a shore phase of marine 

 deposition, a view strengthened by the flat character of the limestone 

 pebbles. From the lithology and the relation to the underlying 

 Wolsey shale this conglomerate is correlated with the Meagher lime- 

 stone, described by Weed in the Little Belt Mountains folio." 



Carboniferous. — " Madison limestone (Mississippian) : Overly- 

 ing the Meagher limestone is a thick mass of calcareous strata that 

 constitutes the great bvdk of the Big Snowy Mountains. This mass 

 may be separated into three distinct lithologic units. The lowermost 

 comprises 200 feet of chocolate-colored limestone, cherty throughout 

 and massive in general appearance, though in reality somewhat thinly 

 bedded. A striking characteristic in connection with this limestone 

 is the strongly fetid odor emanating when struck with a hammer, 

 due no doubt to some form of sulphur. It was supposed in the field 

 that this limestone corresponds to one of similar character in the 



Names of species are as identified by Walcott. 



