﻿Vol. 66.] GEOLOGY OF THE DISTEICT AROUND LLANSAWEL. 411 



abrupt as rock emerges from drift. The beds consist of grey-black 

 shales, much cleaved, and weathering into rusty, earthy fragments. 

 Interbedded with them are grey, banded, gritty partings, a half 

 to 1 inch thick ; these become more conspicuous up the road, and 

 just before the bend attain a thickness of 12 inches. This thicken- 

 ing of the grits is responsible for the well-marked ridge, already 

 mentioned, which gives the only really continuous strike-line across 

 the area. At this point, on the east side of the road, is a small 

 quarry in grits and shales. There are quarries in the same beds 

 at five other points within half a mile to the south-west, and 

 another half a mile away to the north-east ; the largest of these 

 provides an excellent exposure of both grits and shales, 280 yards 

 south-east of Clynmarch. The section is as follows : — 



Thickness in feet. 



(3) Thinly bedded banded grits and sandy grey shales — 



(2) Blue-black shales, cleaved, metallic weathering, ripply 



bedding-surfaces 10 to 15 



(1) Sandy micaceous grits, well bedded, with shaly partings . 30 



This quarry has furnished the following graptolites : — Mono- 

 graptus cyphus, M. revolutus, and Climacograptus tomquisti ; while 

 the quarry to the east of the road has yielded Monograptus cyphus 

 and Climacograptus rectangularis . 



These beds belong, therefore, to the zone of M. cyphus, and we 

 have named them Clynmarch or cyphus Grits and Shales 



Continuing up the road, no more grits are seen, but shales are 

 exposed at intervals in the road and in the bank. On the whole, 

 these appear to be lighter, tougher, and bluer ; but they are inter- 

 bedded with softer black partings, which have yielded a few useful 

 graptolites. Cleavage is still strongly marked, and the dip remains 

 very constant, about 40° north 30° west. 



(C 2 ). — Some 370 yards above the road-quarry were found (L. 14 

 in the map, PI. XXIX) Monograptus gregarius, Lapw., M. jaculum, 

 Lapw. (?), Mesograptus magnus, H. Lapw.(?), Glyptograptus tamar- 

 iscus, Nich., and Climacograptus tomquisti, Elles & Wood. 



Just above this a slight dip occurs in the road, suggesting the 

 presence of softer beds. The small rise which follows is due to 

 dark-grey, rather tough, shales from which no fossils were obtained. 



(C 3 ). — About 300 yards farther on, the rock is a pale mudstone, 

 and weathers to a pale grey with black stains. Rocks of this 

 nature are exposed at intervals for the next 300 yards ; and just 

 beyond the road to the north-east the following fossils were ob- 

 tained in a darker, more shaly bed (L. 15) : — Monograptus cf. becki, 

 M. exiguus, and M. runcinatus. 



These rocks form the road-surface all up Banc Pengelli, and 

 weather into raised hummocky masses ; a quarter of a mile above 

 L. 15 one specimen of Monograptus marri was obtained. 



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