ABSENCE OF DAKOTA CONGLOMERATE. 311 



decidedly arenaceous shale that resembles the shales frequently found in 

 the Dakota of this region; but the typical Dakota conglomerate of more 

 southern localities is entirely wanting, nor is there any distinct sand- 

 stone zone of sufficient importance to replace it. The section of 780 feet 

 to the top of Belt butte shows a series of black carbonaceous shales with 

 sandy and flaggy shales and thin beds of sandstone. Number _!l of the 

 section is a bed of massive, coarse sandrock, 50 feet thick, that forms the 

 "belt" about the butte, and number "24 is a white and hard limestone 

 that forms the upper belt or crown. The top rock is a gray sandstone 

 underlain by black carbonaceous shales. Careful search was made for 

 fossils, but nothing whatever could lie found. 



As noted farther on in this paper, the coal semi passes under the creek 

 (at the mouth of Little Belt creek); and beyond this point to its con- 

 fluence with the Missouri, Belt creek cuts higher strata, the bluffs of the 

 Missouri at fort Benton belonging to the Fort Benton group. 



Descriptive Geology. 



As it was deemed quite important to establish the exact horizon of 

 the coal seam relative to the shales from which the leaf remains were 

 obtained, the beds were traced continuously by means of ledges exposed 

 along the Missouri river and the Avails of Sand coulee from black Eagle 

 falls to the coal mines at Sandcoulee and across the plateau from the 

 latter place to the mines of Belt creek. 



At Black Eagle falls, the first of the series of cascades below the city 

 of Great Falls, the river bluff is about 150 feet high, exposing a good 

 natural section, the rocks of which were even better exposed in the cut- 

 tings made for the dam and for the foundations of the smelter on the 

 western side of the river. Arranged in tabular form, this section is as 

 follows : 



Thickness 

 Hill top, on which the smelter chimney is erected. in feet - 



21. Sandy shale, greenish 20 



•_'(). Sandy shale, red and purple 15 



in. Sa nil nick Ledge, fissile, m 4 prominent 5 



IS. ( 'lay ami red shale 15 



17. ( 'lay and sands, green and gray ;>> 



Hi. ( lay, red and Leafy shale 5 



L5. I ronstone forming caps to sandstone pillars 1 



II. Sandstone; crumbling, weathering into pillars and buttes; this i> hut a 



lens of sandrock in a clay scries LO-30 



L3. Clays L0 



L2. Sandstone ledge ; forms top of river bluff 25 30 



II. Clay-shales, red and gray on weathered slopes, blue-gray in fresh ex- 

 posures 50 



