312 W. H. WEED — TWO MONTANA COAL FIELDS. 



Thickness 

 in feet. 



10. Sandstone ledge, gray and hard 2 



9. Shales, gray or red 15-20 



8. < irav sandstone 5 



7. Limestone, decomposed, brown, splintery 2\ 



6. Shale, easily crumbled, green-gray 5 



5. Sandstone, passing into shales at base 7 



4. Shale and shaly sandstone, rotten, red-brown 9 



.'!. Sandstone, massive ledge, forming fall of river 7 



2. Flagstone, purple and lilac sandrock 12 



1. Sandstone, massive, square block jointing 5 



At the top of the section there is a sandy series (numbers 10-21) whose 

 erosion has formed most picturesque and brilliantly colored miniature 

 badlands. The beds change rapidly horizontally, passing into the lilac 

 sandstone (freestones) and clay-shales, the sandstone being an excellent 

 building material and easily quarried and much used. The clay-shales 

 interbedded with them hold the beautiful ferns identified by Professor 

 Newberry. These beds rest on a massive layer of buff sandrock con- 

 taining thin seams of lignite which, traced southward, is found to corre- 

 spond to the sandrock above the coal seam. This ledge illustrates the 

 difficulty of following a particular ledge of sandstone any considerable 

 distance, for it passes into clays and sands a few miles to the northward, 

 and is not a decidedly recognizable horizon at the south. Beneath this 

 sandrock, forming the top of the bluff, there is an alternating series of 

 clay-shales and sands, which are blue and gray where freshly cut for the 

 walls of the new smelter, but generally weather reddish or brown ; beneath 

 these shales, a ledge of soft granular sandstone caps a series of soft clay- 

 shales, resting upon the lilac-colored or pinkish sandstones forming the 

 falls — rocks that pass laterally into red clays half a mile down stream. 



Traced southward, the upper members of the section are seen to form 

 the slopes about the city of Great Falls, the city dam being built on a 

 sandstone ledge corresponding to number 12 of the foregoing section. 

 South of the city the eastern bank of the Missouri shows exposures of red 

 clays with freestones and shales that are quarried at a number of points 

 between the city and Sandcoulee. At the mouth of the valley known 

 as Sand coulee, where the creek empties into the Missouri, a ledge of 

 white quartzose sandstone outcrops on the slope some 25 feet above the 

 river; it corresponds in horizon to that on which the city is built, and 

 forms a readily traceable ledge, extending up the coulee to the coal mine-. 

 It is capped by rather thinly bedded, square-jointed, lilac or pinkish 

 sandstones and alternating slate beds, which form excellent building- 

 stone. Following these beds upthe coulee the coal seam does not appear 

 until reaching a branch of Sand coulee known as Straight coulee, on 



