204 



LOWER LUDLOW ROCK. 



The Aymestry limestone differs in lithological aspect and useful properties, from any 

 overlying or underlying calcareous rocks, being infinitely less crystalline and pure than 

 the mountain or carboniferous limestone, and inferior in quality, though not in the 

 same degree, to the lower limestone of Wenlock. Again, the Aymestry rock, partaking 

 of the predominant character of the Ludlow formation, is for the most part flat-bedded, 

 and is, on the whole, much less concretionary than the limestone of Wenlock. Its 

 earthy character renders it, however, of very great value as a cement, particularly in 

 subaqueous operations, and in ceiling and plastering, the mortar which is made of it 

 setting rapidly under water. I have not observed any simple minerals in the Aymestry 

 limestone, except crystals of carbonate of lime, and very rarely of sulphate of barytes. 

 In the dislocated quarries on Mocktree Hays, and also at Aymestry, black siliceous 

 and cherty matter sometimes penetrates the interior casts of the fossils. 



Lower Ludlow Rock. (PI. 31. fig's. 2, 3, 4, and 5. and d. of wood-cut p. 196.). 



The strata distinguished by this name are seen in the lower parts of the escarpments, 

 underlying the Aymestry limestone. They differ from those of the upper Ludlow Rock, 

 in being more argillaceous, less sandy and calcareous, with rarely a trace of mica. 

 They constitute, in fact, a great argillaceous mass, strictly entitled to the provincial 

 name of "mudstone 1 ." The colours vary from light to dark grey and black; but 

 whatever may be the tints of the rock when first quarried, it usually weathers to the 

 same light ashen colour which is seen all over the surface of the Upper Silurian Rocks. 

 The beds immediately beneath the Aymestry limestone, are occasionally wrought for 

 flags, being sometimes slightly calcareous, and rather more sandy than the remainder 

 of the subgroup. Quarries of these flagstones may be seen at the Garden House 

 quarries near Aymestry, and in the hills east of Leintwardine, Mocktree Forest, &c, 

 and at which places they are called " Pendle " by the workmen. This flaglike structure 

 is due to fine lamina? of sandy matter separating the argillaceous layers. Occasionally 

 these flagstones are separated from the overlying Aymestry limestone, by courses of a 

 saponaceous clay (in many instances a complete fuller's-earth) , of a yellowish white 

 and grey colour, which is commonly known throughout Herefordshire and the adjacent 

 counties under the name of " Walker's earth, or soap," and is sometimes used by the 

 country people for cleansing purposes. Beds of this " Walker's 2 earth" are not in- 



1 In the Abberley hills and at other places, the rocks of this age and character are called mudstones, from 

 their tendency to dissolve into mud. In the south-western parts of Salop, and adjoining parts of Montgomery- 

 shire, they are termed gi^eenstones. In a third district, they are known as waterstones. The most expressive 

 of these provincial names is mudstone. In the sequel it will be shown that this term is generally applicable to 

 the Upper Silurian Rocks. 



2 " Walker Erde ", the German of fuller's earth, is evidently the origin of this provincial name. A Walk, 

 or Walker's Mill, is still used occasionally instead of Fuller's Mill; hence "Walker's Earth," or "Walker's 

 Soap." 



