MUDDY S OILS OF THE LOWER LUDLOW ROCKS. 263 



III. Primary Strata. — In these rocks slates abound, and lime- 

 stones are more rare. Organic remains are also less frequently met 

 with than in the superior rocks. These remains belong all to extinct 

 species, the greater part to extinct genera and families, and are frequent- 

 ly so wholly unlike to existing races that it is often difficult to trace any 

 resemblance between l.\e animals which now live and those which appear 

 to have inhabited the waters of those ancient periods. 



F. — Silurian System. 



18°. Upper Silurian. 3800 /^ The upper Ludlow rocks consist of 



1°. Ludlow formation. sand-stones more or less calcareous and 



a Upper Ludlow ) argdlaceous. These rest upon hard, 



b Aymestry Lime-stone i 2000 somewhat crystalhne, earthy hme-stones 



• tf Lower Ludlow ) (Aymestry hme-stones.) The lower 



'' Ludlow rocks are masses of shale more 



2°. Wenlock formation. free from lime and sand than the upper 



^ ~'Pl^"S*°"® \ 1800 beds, and from the mode in which they 



Shale ) decay into 7nnd are locally known by 



the name of " mud-stones." 



The Wenlock or Dudley formation 

 consists in the upper part of a great 

 thickness of lime-stone beds often argil- 

 laceous, and abounding in the remains 

 of marine animals; and in the lower 

 part of thick beds of a dull clayey shale 

 — in its want of cohesion, and in its 

 mode of decay, very much resembling 

 the mud-stones of Ludlow. 

 Extent. — The principal seat of these rocks in our island is in the eastern 

 counties of Wales, where they lie immediately beneath the surface over the 

 eastern half of Radnor, and the north of Montgomery. 



Soil. — The prevailing character of the soils upon these formations is derived 

 from the shales and mud-stones — and from the earthy layers of the sand-stones 

 and lime-stones which decay more readily tlian the purer masses of these rocks. 

 The traveller is immediately struck in passing from the rich red marls and 

 clays of the old red sand-stone in Hereford, on to the dark, almost black, soils 

 of the upper and lower Ludlow rocks in Radnor, not merely by the change of 

 colour, but by their obviously diminished value and productiveness. The up- 

 per Ludlow is crossed by many vertical cracks and fissures, and thus, though 

 clayey, the soil 'which rests upon it is generally diy, and susceptible of cultiva- 

 tion. 



Not so the muddy soils of the lower Ludlow and Wenlock rocks. They are 

 generally more or less impervious to water, and being subject to the drainage 

 of the upper beds, form cold and comparatively unmanageable tracts. It is Only 

 where the intermediate lime-stones (Aymestry and Wenlock lime-stones) come 

 to the surface and mingle their debris with those of the upper and lower rocks, 

 that the stiff clays become capable of bearing excellent crops of wheat. This 

 fact, however, indicates the method by which the whole of these cold wet clays 

 might be greatly improved. By perfect artificial drainage and copious limeing, 

 the unproductive soils of the lower Ludlow and of the Wenlock shales might be 

 converted into wheat lands more or less rich and fertile. It unfortunately hap- 

 pens, however, that in those districts of North and South Wales, where the 

 dark grey or black " rotchy'^ land of the mud-stones prevails, lime is often so 

 scarce, or has to be brought from so great a distance, as to render this means of 

 improvement ahnost unattainable. 



