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PROCEEDINGS 0E THE GEOLOGICAL SOCIETY. [Apr. 10, 



place is quite level, and strewn with an immense profusion of 

 boulders, being at the base of the Third great Prairie-level. The 

 sides of this valley are cut by numerous ravines, which only extend 

 a short way back into the prairie, and exhibit sections of the 

 following strata (see fig. 4) : — 



Fig. 4. — La Roche Percee, in the Valley of the Souri River : a section 

 of the Tertiary Lignite Group. 



a. Drift. b. Splintery limestone. c. Clay with lignite. 



cl. Coarse-grained sandstone. e. Concretionary sandstone. 



a. Drift with boulders 4 to 7 feet. 



b. Mud-stone 1 foot. 



c. Incoherent sandstone, fine-grained, with hard con- 



cretions impregnated with iron, which weather 



concentrically 10 feet. 



d Porous calcareous sinter 1 foot. 



e Hard blue ironstone-shale, decomposing into deep 



orange-coloured splinters 2| feet. 



/ Gritty limestone 2 „ 



g Ash-coloured clay in thin indistinct layers, very soft, 



with one bed of lignite 9 inches in thickness 8 „ 

 h Hard blue limestone 



i Same as g, but with thin seams of lignite 10, 8, and 



6 inches in thickness 15 ,, 



1c. Gritty limestone 2 „ 



Brightly coloured marls and shales, with selenite in 



small fragments 10 „ 



in. Coarse-grained, incoherent sandstone more than. ... 20 „ 



Excepting a few fragments of plant-impressions, like stems of 

 sedges, no fossils were obtained from these beds by which the age 

 could be identified. They may perhaps be passage-beds, representing 

 the highest strata of the Cretaceous era, overlain by the lignite-basin ; 

 as further south they are so disposed, and with very similar mineral 

 characters. 



The lignite does not occur in well-defined beds, but graduates into 

 the shales on both surfaces. It is not visible until a light ashy deposit 

 is removed from the exposed edge of the bed, which has been formed 

 by the soft clay washing down from the strata above. The lignites 

 are of several different varieties, some having quite the texture of 

 compact canncl-coal of fine quality, some like the more glistening 



