54(J Murchisons Silurian System. 



form alone, they constitute the cornstones of the inhabitants, and 

 in this state are quarried exclusively for the repairs of the roads, and 

 are not burnt for lime. The best courses are, however, almost crysta- 

 line, and if polished might be considered not inelegant marble, though 

 the concretions are usually too small to afford large slabs. In some 

 of the great works at Ditton and Abdon there are two zones, the 

 lowest and largest of which is quarried to a depth of twenty feet, in 

 caverns under the slopes of the Brown Clee Hills. It is needless to 

 mention other localities in this neighbourhood, for the formation here 

 ranges over a very wide area. Throughout the whole of its range, with 

 the exception of this space between the coal field and the older rocks 

 of Csermarthenshire, and its protrusion through some of the poor coal- 

 fields of Bewdly Forest, the strata of this cornstone are very little 

 inclined, an arrangement which might naturally have been looked for in 

 the central parts of a basin or triangle of large size. The spotted marls 

 can never be distinguished from those of the new red sandstone, 

 except perhaps when they are separated from each other by beds of 

 hard micaceous sandstone. In districts where the argillaceous cha- 

 racter exclusively predominates, there is some difficulty in persuading 

 the inhabitants that they live upon the old red sandstone, although that 

 name, when applied to the whole system, is as unobjectionable as any 

 in the nomenclature of geology. 



" Whenever the order of superposition is not apparent, the fragments 

 of fossil fishes, which occur in abundance throughout the cornstones, 

 constitute the best distinction between this formation and the lower 

 new red sandstone, which it so much resembles. These fishes, which will 

 be described in a subsequent chapter, are of very peculiar forms, and 

 their fragments being often of brilliant purple and blue colours, are 

 excellent points of attraction for the eye of the geologist, since they 

 present a strange contrast to the surrounding dull red and green matrix 

 in which they are enveloped." 



We have given Mr. Murchison's detailed account of the 

 cornstone in his own words, because we have yet to discover 

 this member of the old red system in India. The fishes al- 

 luded to as characteristic of this rock in Britain, are various 

 species of Cephalopsis, Ag. whose form somewhat resembled 

 the Siluridae ; one of the most perfect examples that has 

 been found is that of Ceph. Lyellzi ; we need not here give a 

 figure of it, as it is already represented in Lyell's Geology 



