GEOLOGY OF CENTRAL WALES. 



145 



From the Bryn-y-Carnau Quarry near the old "Water-reservoir, 

 Aberystwyth. 



Monograptus Sedgewickii, Portl. 



erenularis, Laptop 



lobiferus, M'Coy. 



Monograptus tenuis ? 

 Dictyonema delicatuluni, Lapw. 

 (n. sp.). 



But the most important zone of fossils is found somewhat higher 

 up in the series, exposed in a quarry formerly worked for building- 

 stone and road-metal, in a field below Cefn Hendre, where we have 

 collected 



Monograptus Sedgewickii, Portl. 



, Tar. distans, Portl. 



Clingani, Carr. 



lobiferus, M' Coy. 



turriculatus, Barr. 



Monograptus Hisingeri, Carr. 



tenuis, Portl. ? 



Oi'tlioceras, sp. 

 Calymene. 



Many of these fossils were found in a set of thin, dark-grey, mica- 

 ceous flags (the large-flag series), which are sometimes to be obtained 

 of large size (4-6 feet square). 



Dips and Foldings. — Many rock-foldings, some of them very 

 violent and accompanied by fractures, are seen in our line of 

 section, good examples being exposed near the second milestone 

 from Aberystwyth ; so that for a mile and a half along the Upper 

 Devil's Bridge-road we appear to have only the same set of beds, 

 repeated again and again by a number of rock-foldings (see section, 

 fig. 1). But beyond this the easterly dip becomes more constant, 

 and we appear to be traversing the outcrop of a continually ascend- 

 ing series. 



2. The Metalliferous-slate Group. — In the Cefn-Hendre quarry, 

 only about a mile and a half east of Aberystwyth, we already find a 

 larger proportion of shales to grits than in the coast-section around 

 Aberystwyth ; and this change becomes still more marked in another 

 quarry on the road-side further on down the hill towards Gogerddan. 

 The same gradual though not perfectly regular disappearance of 

 the grits to the east may be seen in our present section along the 

 Devil's-Bridge road, as, indeed, in any other of the east and west roads 

 from Aberystwyth*. 



A change in the character of the argillaceous rocks appears in 

 regular correlation with the loss of the grits. They become more 

 and more indurated and cleaved, until, as the boundaries of the 

 grit-series are reached, the normal cleavage of the district (striking 

 N.N.E. and S.S.W.) is found even in the partings between thick 

 grit-beds. Thus gradually do we enter into the territory of our 

 second series — the Metalliferous Slates. 



The hills of this district are barren and desolate, even more so 

 than in the Aberystwyth-grit country ; but they are decidedly more 

 rounded and regular in their contours. Here, in the uplands, is a 



* The limit of the grit series may be placed, as indicated by the yellow dots 

 upon the Survey Map, at about three miles and a half east of Aberystwyth. In 

 my pocket-book I find " at three miles from town, grits fewer and thinner than 

 at Aberystwyth," at four miles "a few grit-beds as much as 6 inches thick," and 

 at five miles " still a few thin grits." 



