GRADATION'S FKOM CONTINENTAL TO MARINE CONDITIONS IN CENTRAL MONTANA. 



13 



Log of well drilled hij the Chicago, Milwaukee & St. Paul Railway Co. at Vananda, in sec. 5, T. 7 N., R. 38 E., Mont., 



between October 23, 1913, and October 17, 1914. 



[Elevation of mouth of well, 2,704 feet above sea level.] 



Formation. a 



Driller's description. 



Thick- 

 ness. 



Depth. 



Judith River formation. 6 



Shale, sandy 



Sand; 30 gallons of water an hour. 



Shale, yellow 



Sand 



Shale and sand . 



Sand 



Shale, yellow. . 

 Sand 



Sand and shale 



Shale, blue 



Sand; flow of alkaline water, 2,400 gallons an hour. 



Feet. 

 23 



7 

 16 

 11 

 24 



8 

 16 

 14 

 24 

 46 

 26 



Feet, 



23 



30 



46 



57 



81 



89 



105 



119 



143 



189 



215 



Claggett shale. <= 



-(d)- 



Colorado shale. 



Kootenai (?). 



Shale; disintegrates when exposed to air. 



Shale, « black surface; whitens on exposure to air , 



Shale 



Oyster-shell rim, fossil determined by former State geologist 

 of South Dakota as Inoceramus labialus. 



Shale, dark brown 



Hard rock 



Shale, soft; color changes on exposure from dark to light brown. 



Shale, light brown 



Slate 



Soapstone 



Shale, white 



Shale, dark 



Shale, black 



Shale, brown 



Shale, dark, caving. 



Slate, caving 



Limestone 



Shale 



Shale and lime shells 



Shale, soft, caving 



Shale and lime shells 



Shale, soft, caving 



Shale, dark 



Shale and lime shells 



Sandstone, hard 1 



Limestone, black, sandy I May represent the Mowry shale mem- 

 Limestone I ber. 



Slate 



Sand, water bearing; water rose within 50 feet of surface. 



Sandstone, compact 



Limestone 



Shale, white 



Shale, red 



Shale, white 



Shale, red 



Shale, white 



Shale, red 



685 



140 



907 



5 



107 

 29 

 32 

 40 

 40 

 13 

 23 

 45 

 19 



100 

 31 

 19 

 41 



239 

 15 

 35 

 20 



105 

 35 



103 

 32 

 18 

 42 

 55 



10 

 30 

 19 

 23 



7 

 8 



27 

 8 



35 



900 



1,040 



1,947 

 1, 952 



059 



088 



120 



160 



200 



213 



2,236 



2,281 



2,300 



2,400 



2,431 



2,450 



2,491 



2,730 



2, 745 



2,780 



2,800 



2,905 



2,940 



3,043 



3,075 



3,093 



3,135 



3,190 



3,200 

 3,230 

 3,249 

 3,272 

 3,279 

 3,287 

 3,314 

 3,322 

 3,357 



a Correlation revised by author. 



b Called Lance in log furnished by railway company. 



c Called Pierre in log furnished by railway company . 



d In view of the lithologic similarity between the Claggett and Colorado the position ol this boundary must be regarded as uncertain. 



e Called Niobrara in log furnished by railway company. 



