274 DESCRIPTIVE GEOLOGY. 



in the centre, rise 1,500 feet above its bed, gives an excellent section of the 

 sandstones and limestones of the Upper Coal-Measures. The dip of the 

 beds in this canon is 27° to the northeast, which is not quite as steep as that 

 of the ridge to the north. 



At the lower end of the canon, some croppings of red quartzite are 

 found under the Tertiary benches of Brown's Park ; but in the canon itself 

 the main exposures belong to the Upper Coal-Measure group, of which a 

 thickness of about 2,100 feet is shown. They consist of a lower portion of 

 about 500 feet of drab limestones and sandstones, above which is a bed of 

 pinkish sandstone of about 100 feet in thickness; and then 1,500 feet of light- 

 colored strata, very regularly and rather thinly bedded, consisting of lime- 

 stones and sandstones, with intermediate grades, in which the siliceous 

 material seems, in general, to predominate over the calcareous. Included in 

 this series are numerous thin beds of cherty material, one of which, of about 

 4 inches in thickness, was particularly prominent by its black color, which 

 gave it the appearance of coal ; other seams contained considerable amounts 

 of iron oxide. An analysis, made by Mr. B. E. Brewster, of one of the 

 lower beds, a fine-grained drab limestone, having a fracture like a litho- 

 graphic limestone, gave the following results : 



Silica 2.021 



Alumina and Ferric oxide . . . 0.569 



Lime 54 064 



Magnesia 0.338 



Carbonic acid 42.851 



Water and organic matter : . . 0.415 



100.258 

 The upper gate of the canon is formed by a bed of cherty limestone, 

 whose surface is marked by abundant silicified casts of fossils. Among the 

 collections made in this bed, the following have been recognized : 



BelleropJion carbonarius. 

 Sedgivickia concava. 

 Nucula parva. 

 Fleurotomaria, sp. ? 

 Fusilina, sp. ? 



