SOILS OF THE MAGNESIAN LIMESTONE AND COAL MEASURES. 249 



13°. Magnesian Limestone. The magnesian lime-stone is gene- 



rally of a yellow, sometimes of a ;D;rey, 

 colour. In the upper part it occasion- 

 ally presents itself in thin beds, which 

 crumble more readily when exposed to 

 the air. In some places, also, it assumes 

 a marly character, forming masses 

 which are soft and friable ; in general, 

 however, it is in thick beds, hard and 

 compact enough to be used for a build- 

 ing stone or for mending the roads. The 

 quantity of carbonate of magnesia it 

 contains varies from 1 to 45 per cent. 

 It is in the north of England generally 

 traversed by vertical fissures, which ren- 

 der the surface dry, and make water in 

 many places difficult to be attained. 

 Extent. — The magnesian limestone stretches in an almost unbroken line 

 nearly due north from the city of Nottingham to the mouth of the river Tyne. 

 It is in general only a few miles in width, its principal expansion being in the 

 county of Durham, where it attains a breadth of 8 or 10 miles. 



Soil. — It forms, for the most part, a hilly country, covered by a reddish 

 brown soil, often thin, light and poor, where it rests immediately on the native 

 rock — producing indifferent herbage when laid down to grass, but under skilful 

 management capable of yielding average crops of turnips and barley. In the 

 eastern part of the county of Durham tracts of the poorest land rest upon this 

 rock, but as this formation is for the most part covered with deep accumulations 

 of transported materials — the quality of the soil is in very many plv^ more 

 dependent upon the character of this superficial covering than upon tTOnature 

 of the rock beneath. 



During the slow degradation of this rock, the rains gradually wash out great 

 part of the magnesia it contains, so that it seldom happens that the soil formed 

 from it, though resting on the parent rock, contains so much magnesia as to be 

 necessarily hurtful to vegetation. 



D. — Carboniferous System. 



14°. Coal Measures. 3i}0ft. Consisting of alternate beds of indu- 



rated bluish-black clay (coal shale), of 

 siliceous sand-stone generally grey in 

 coiour and containing imbedded plants, 

 and of coal of various qualities and de- 

 grees of thickness. Beds of lime-stone 

 rarely appear in this formation till we 

 approach the lowest part of the series. 

 Extent. — Fortunately for the mineral resources of Great Britain, the coal 

 measures occupy a large area in our island. Most of the districts in which 

 they occur are so well known as to require only to be indicated. The south 

 Welsh coal-field occupies the south of Pembroke, nearly the whole of Glamor- 

 gan, and part of Monraouth-shire, In the north of Somerset are the coal mea- 

 sures of the Bristol field, which stretch also across the Severn into the forest of 

 Dean. In the middle of the central plain of the new red sand-stone, lie the coal- 

 fields of Ashby-de-la-Zouch, of Coventry, and Dudley, and on its western 

 borders are those of Shropshire, Denbigh, and Flint (North Wales), To th« 

 north of this plain extends on the right the Yorkshire coal-field from Tfotting- 

 ham to Leeds, while on the left is the small coal-field of Newcastle-under-Line, 

 and the broader Lancashire field which crosses the country from near Liverpool 

 to Manchester. Almost the entire eastern half of the county of Durham, and 



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