Yol. 62.] TARANNON SEEIES OF TARANNON. 653 



horizons. Owing, however, to the deformation which the beds have 

 undergone, they are, as a rule, difficult of extraction and poorly 

 preserved, and are practically confined to the darker grey or black 

 shale-bands. 



II. Stratigraphical Relations of the Rocks in the 

 Tarannon District. 



(A) Description of the Typical Section in the 

 Tarannon River. 



The valley-course of the Tarannon River affords the longest, the 

 most continuous, and, on the whole, the most satisfactory section in 

 the district. It rises near Llyn Gloew in the centre of the Tarannon 

 moors, and flows thence first southward across the central part of 

 the tableland itself ; then south-eastward down its flanks ; and 

 finally, eastward beyond the base of the tableland, to join the Severn 

 at Caersws. 



(1) Wenlock Series (C). 



(i) Pynyddog Grits (Cb). 



All the central part of this Tarannon tableland, over which the 

 Tarannon River flows for the first 2 miles or more, is occupied by 

 the Denbighshire Grits ; but, owing to the boggy nature of the 

 ground, the bed-rock is exposed at the surface only in isolated 

 patches. Wherever rocks are seen, however, they consist of grey 

 felspathic and micaceous grits varying in thickness from a few inches 

 to several feet, separated by bluish-black mudstones, shales, and 

 flags. Many of the beds show marked concretionary structure, and 

 frequently weather to a brilliant orange colour. These strata, 

 which are identical with those of the great sheet of Denbighshire 

 Grits in the country to the north, may be termed the Fynyddog 

 Grits, from the heights of Newydd Eynyddog. 



They are well exposed in the river-course close to the farmstead 

 of Tarannon, where they dip east-north-eastward at an angle of 23°, 

 while fairly-massive grits are seen both in the river-bed and also 

 protruding through the peaty ground on both sides for some distance 

 down the stream. Judging from the form of the ground, we may 

 infer that these Fynyddog Grits are continued as far as the sheep- 

 fold, nearly 1 mile below the Tarannon farmstead, and in this part 

 of the district they must have a thickness of at least 1500 feet. 

 No search for fossils has yet been made in these beds. 



(ii) Nant-ysgollon Shales (Ca). (Zone of 

 Cyrtograptus Murch isoni.) 



As we follow the river southward the grits disappear, and we find 

 coming out from below a broad band of flaggy shales and mudstones 



