830 



COAL 



though loss tenacious than that mineral ; and, when burnt, exhaling but slightly tho 

 vegetable odour so peculiar to all imperfeetly-bituminised substances. Tho fossil 

 remains of shells and plants provo the Brora coal to be cinalogousto that of the eastern 

 moorlands of Yorkshire, although the extraordinary thickness of the former, com- 

 pared with any similar deposit of tho latter (which never exceeds from 12 to 17 

 inches), might have formerly led to tho belief tluit it was a detached and anomalous 

 deposit of true coal, rather than a lignite of any of tho formations above tho Now Red 

 Sandstone : such misconception might more easily arise in tho infancy of geology, 

 when the strata were not identified by their fossil organic remains. 



The beds of coal at Brora have been recently (1873) opened up more thoroughly 

 for tho Duke of Sutherland, M'ith a view to supplying the district with fuel. Tho 

 latest report, August 1873, says : ' The output of coal at the Duke of Sutherland's 

 colliery at Brora is as yet small, but it is very satisfactory as regards quality and in 

 the promise of quantity. In the seam which is at present being worked there is a 

 narrow band about three inches thick, which is somewhat sulphurous ; but this can 

 easily be chipped off and detached. From various causes, it is at present inconvenient 

 to supply the public with coals at the pit mouth, and due notice will be given when 

 the workings are in such a condition as to admit of the public being freely supplied. 

 A few weeks ago a 6-ton truck of Brora coal was sent south to Inverness ; and coal 

 has also been supplied from the mine to the inhabitants of Laing and tho eastern 

 districts of Sutherlandshire at about ll. and in some cases rather loss, per ton. This is 

 only about half the price paid for coal from the south. The Duke of Sutherland's 

 lime-kilns at Laing are now almost constantly supplied from the Brora mine. When 

 the new seam is opened up and worked, it is expected that the supply will be both 

 regular and plentiful.' This expectation does not appear to have been realised (1874). 



For description of the oolitic coals of Scotland, see Mr. J. Judd's paper on ' The 

 Secondary Rocks of Scotland,' in ' Quart. Journ. Geol. Soc.', Lond. xxix. 1873, p. 97- 



On the coast of Yorkshire the strata of a similar formation appear in tho 

 following descending order, from Filey Bay to Whitby : 1. Coral-rag. 2. Calca- 

 reous grit. 3. Shale, with fossils of the Oxford clay. 4. Kelloway rock (swelling 

 out into an important arenaceous formation). 5. Cornbrash. 6. Coaly grit of Smith. 

 7. Pierstone (according to Mr. Smith, the equivalent of the great oolite). 8. Sand- 

 stone and shale, with peculiar plants and various seams of coal. 9. A bed with fossils 

 of the inferior oolite. 10. Marl-stone? 11. Alum-shale or lias. All the above strata 

 are identified by abundant organic remains. 



The most complete and simplest form of a coal-field is the entire basin-shape, 

 which we find in some instances without a dislocation. An example of this is to be 

 seen at Blairongone, in the county of Perth, immediately adjoining the western 

 boundary of Clackmannanshiro, as represented in fig. 467, where tho outer elliptical 



467 



470 



East B 



c J\ \ A West EastB 



469 



AWest 



line, marked A, B, c, D, represents the crop, outburst, or basset edge of the lower 

 coal, and the inner elliptical line represents the crop or basset edge of tho superior 

 coal. Fig. 468 is the longitudinal section of the line A B ; andjfy. 469, the transverse 

 section of the line c D. All the accompanying coal -strata partake of the same form 

 and parallelism. These basins are generally elliptical, sometimes nearly circular, 

 but are often very eccentric, being much greater in length than in breadth ; and 

 frequently one side of the basin on the short diameter has a much greater dip than 

 the other, which circumstance throws the trough or lower part of tho basin concavity 

 much nearer to the one side than to the other. From this view of one entire basin, it 



