180 GEOLOGICAL SUEVEY OF THE TEEEITORIES. 



The basis of this division is partly chemical and partly structural, the 

 genera being derived from differences in chemical constitution, while 

 the species are made with reference to the physical properties of the 

 coals. Thus he separates all coals into — 



1. Anthracites containing 2 to 10 per cent, of gaseous matter, of 

 which 1 to 2 per cent, is water ; ash in any ratio; specific grav- 



I. { ity 1.50. 



2. Semi-anthracites containing 7 to 8 per cent, of volatile combusti- 

 ble matter; does not intumesce. 



1. Bituminous ; carbon, 52 to 84 per cent.; volatile substances 16 



TT J to 48 per cent.; ash, 2 to 20 per cent.; specific gravity, 1.269. 



' f 2. Semi-bituminous; volatile substances more than 11 to 12 per 



[ cent, and less than 18 per cent. 



TTT ( Hydrogenous; volatile substances, 30 to 70 per cent., specific 



li1, \ " gravity, 1.272. 



These varieties are further split up, in the case of bituminous, into la, 

 caking coal; 16, cherry coal; and lc, splint coal. The semi-bituminous 

 into 2a, semi-bituminous cherry coal; and 2b, semi-bituminous splint 

 coal. The hydrogenous, 1, cannel coals ; 2, hydrogenous shaly coals, 

 (Torbanehill, &c.;) and, 3, asphaltic coal, (Albert mine.) 



This classification takes no account of the age of the coals, but merely 

 considers the nature of the mineral. Accordingly it will be found con- 

 venient of application to coals about whose age there is yet some differ- 

 ence of opinion among geologists. 



Mode of occurrence. 



The coal of the Eocky Mountains is distributed along their flanks 

 as several leaves in the great book of folded strata and invariably 

 in the transition beds or between the tertiary and cretaceous. No- 

 where in the world is there such a vast development of the recent 

 coal measures, and in few places is their existence more necessary 

 to the advancement and improvement of the region in which they occur. 

 They lie regularly and in the main quite horizontally, though close to 

 the mountain the beds are naturally tilted. The coals are called vari- 

 ously lignites, brown, semi-bituminous and bituminous, though from 

 their chemical constitution they ally themselves much more nearly with 

 the latter. They are distinguished by their cleavage planes, which latter 

 are nearly perpendicular to the planes of lamination and to each other, 

 and give to the coal (which is usually friable) a stair form structure, 

 almost resembling the crystallization of some clusters of iron pyrites. 

 It is hardly worth while to say that these coals differ in different local- 

 ities as to general structure and chemical composition. 



It would be an exceedingly interesting piece of work to follow up 

 those beds from their easternmost outcrop westward and to seek to 

 identify them in their different plications. Paleontologically these coals, 

 containing almost exclusively plant fossils, comparatively few shells 

 have been discovered, and those of species which leave the real question 

 of u cretaceous or tertiary " undecided. The great mass of the fossils 

 are of deciduous leaves, very much resembling now existing varieties. 

 Broad leaves like the oaks and even nuts transformed into dull red 

 sandstone (San Lazaro) (in one case showing the kernel and shell beau- 

 tifully distinct from each other, where a fracture of the latter had ex- 

 posed the former to view) are met with in the drab clay and more espe- 

 cially in some dark-colored sandstones near the coal. Here, almost on 



