DISTRIBUTION OF THE STEATA. 451 



grained sandstone, with alternating bands of red and green 

 argillaceous marls. 



(a). The picturesque cliffs of Symond's Tat, between 

 Monmouth and Ross ; on the right bank of the Wye, to the 

 north of Tintern Abbey ; and along the summit of Went- 

 wood, between Chepstow and Usk. 



(b). The Tan bwlch-y-chwyth, near Trecastle; the Daren, 

 two miles north of Crickhowell. 



Fish Holoptychius nobilissimus. 



II. COENSTOKE AND MAEL. 



Bed and green argillaceous and spotted marls, with alter- 

 nating bands of sandstone, or with irregular courses of con- 

 cretionary impure limestone (Cornstone), mottled, red, and 

 green. 



The cliffs under the castle at Lanstiphan, near the mouth 

 of the Towy ; in the vicinity of Hay ; and in the valley of 

 the Usk, near Abergavenny. 



Fishes -Cephaiaspis and OncTius. 



III. TlLESTOKE. 



Finely-laminated, hard, reddish or green, micaceous, 

 quartzose sandstones, which split into tiles ; with occasional 

 beds of reddish shale. 



In the gorge of the Teme, between Ludlow and Downton 

 Castle, near the Tin Mill; Oakley Park, Ludlow. Horeb 

 Chapel ; the valley of the Cwm Dwr, between Trecastle and 

 Llandovery. 



Fishes Dipterus, Onckus, and various genera of Mollusca. 



In Scotland this system is also largely developed, in Caith- 

 ness and Cromarty, as described by Mr. Miller ; * in Dura 

 Den, south of Cupar, in the valley of Strathmore and adja- 

 cent district, as observed by Sir C. Lyell.f 



* Hugh Miller, Old Red Sandstone, 

 j* Elements of Geology, vol. ii., page 148. 



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