170 



DIVISIONS OF THE OLD RED SYSTEM. 



both by lithological characters and zoological contents,) is surmounted by one red 

 group ; so is it underlaid by another, this lower red group being infinitely thicker than 

 the upper. The chief reason, perhaps, why the Old Red Sandstone has not been con- 

 sidered as entitled to the rank of a system is, that in France and Germany its equiva- 

 lents are ill, if at all, developed. It has, however, been recognised in Poland and Si- 

 lesia, while in Norway there are mountain ranges very similar in structure to the types 

 of this system in the North of England, Scotland, and Ireland. As, however, there is 

 no region of Europe yet examined, where the Old Red Sandstone is better exhibited 

 than in the British Isles, so there is no part of the kingdom in which it is so much ex- 

 panded as in the country here described. Occupying the largest portion of Herefordshire 

 and the adjacent districts of Worcestershire and Shropshire, it spreads over wide tracts 

 of Monmouthshire, surrounding the coal-field of the Forest of Dean ; and forming a 

 girdle round the great South Welsh coal basin, it constitutes in Brecknockshire the 

 ]oftiest mountains of South Britain. The enormous thickness of the red stratified de- 

 posits, included between the coal measures and the Silurian rocks, will at once be com- 

 prehended by any observer who places himself on the eastern slopes of the latter on the 

 Welsh borders of Herefordshire (near Kington, for example); whence casting his eye to 

 the south and south-east, the circle of vision, although extending over all the mountains 

 between the Wye and the Usk, and terminating only in the lofty mountains, called the 

 Brecon and Caermarthen fans 1 , 2500 feet above the sea, embraces nothing but Old Red 

 Sandstone! (See vignette, head of the chapter.) This view does not include a wide 

 superficies, occupied merely by undulating masses of the same strata, but a territory in 

 which successive members of the system rise from beneath each other in distinct moun- 

 tainous escarpments. The same succession, though in a much smaller scale, is dis- 

 played in Shropshire, between the coal-field of the Clee Hills and the older rocks of 

 Ludlow ; whilst in the central districts of Herefordshire the strata lie in a great basin, 

 the lower edges of which are turned up against the Silurian rocks, both on their eastern 

 and western flanks. 



For the convenience of description, a triple subdivision of this system is adopted j 

 the strata being described in descending order under the following names 2 : 



1 . Quartzose Conglomerate and Sandstone, 



2. Cornstone and Marl. 



3. Tilestone, 



they agree in order and in characters with the older strata of the British series ; but as I shall hereafter show, 

 that the Silurian System is there largely — perhaps fully developed, so we have every reason to suppose that 

 the mountain masses of the red conglomerate and sandstone of that kingdom represent our Old Red System. 

 Pusch, indeed, has shown the existence of Old Red Sandstone in Poland, and it is supposed to rise from beneath 

 the coal-fields of Bohemia and Silesia. To what extent does it exist in Russia ? 



1 " Fan :" Anglice, a covering or cap, i. e. the summit. 



2 A similar subdivision of the Old Red Sandstone was first proposed by Buckland and Conybeaie in 'their 

 memoir on the Bristol district. 



