112 DEVONIAN GROUP. 



DEVONIAN GEOUP ; OR, OLD RED SANDSTONE. 



1. Conglomerate and Sandstone. 2. Cornstone and Marl. 

 3. Tilestone. 



The strata comprising this division consist chiefly of 

 various beds of conglomerate, sandstone, marl, limestone 

 and tilestone, alternating with each other, and varying in 

 their characters according to the locality. The name is 

 derived, from this system being extensively developed in 

 Devonshire. A triple subdivision has been adopted by 

 Sir R. I. Murchison, (Sil. Syst.) 



1. QuARTZosE Conglomerates and Sandstone. 



{a) The upper beds consist of quartzose grits, with a slight calcareous 



cement, or pink and reddish quartzose conglomerates, passing 

 {b) downwards into chocolate, brown, and reddish coarse-grained 



sandstone, with alternating bands of red and green argillaceous 



marls, 

 (a) The picturesque cliffs of Symonds Yat, between Monmouth and 



Ross. On the right bank of the Wye to the north of Tintem 



Abbey, and along the summit of Wentwood, between Chepstow 



and Usk. 

 {b) The Fan bwlch-y-chwyth, near Trecastle. The Darem, two 



miles north of Crickhowell. 



Fish. — Iloloptychms nobilissimus. 



2. Cornstone and Marl. 



Red and green argillaceous and spotted marls, with alternating bands 

 of sandstone, or with irregular courses of concretionary impure 

 limestone (Cornstone) mottled, red and green. 



