

Vol. 67.I ASSOCIATED ROCKS OF NORTH-EAST MONTGOMERYSHIRE. 431 



the Gaerfawr Grits on the one hand, and the Llandovery con- 

 glomerates on the other, were laid down. 



These beds do not crop out anywhere in the eastern portion 



of the area, except under the 

 Pentamerus Limestone at Cefn near 

 Buttington. A small outcrop of 

 shales is exposed in the old 

 quarries near Buttington Station. 

 Here the strata fail to exhibit the 

 peculiar character of the Gwern- 

 y-brain Shales, and lack the jet- 

 blackness which is so conspicuous 

 in those beds. They are nearly 

 vertical, and yielded Climacograptus 

 latus (Elles & Wood), a graptolite 

 which is typical of the highest 

 horizon in the Bala Beds. The 

 strata rest upon grits, which appear 

 to belong to the Upper Gaerfawr 

 Series. 



(B) Silurian Eocks. 



(1) Powis- Castle Group. — 

 This important series of massive 

 conglomerates, grits, and sand- 

 stones, with calcareous horizons, is 

 well named after Powis Castle — 

 since that structure is built of 

 materials derived from these rocks, 

 and is founded upon the finest ex- 

 posure of them in the district. 



In Powis Park, the series forms a 

 sharp but broken anticline, on the 

 eastern limb of which the Castle is 

 built. Murchison was under the 

 impression that these beds were the 

 highest in his series of Caradoc 

 Sandstones. I cannot do better 

 than reproduce his section (fig. 4). 

 The western limb of the section 

 is indistinctly lettered under the foliage. The beds are [1] loc. 

 supra cit. : — 



' a. Purplish-brown calcareous grit with many fragments of encrinites in 

 beds, from 8 inches to one foot and a half, with wayboards of red 

 shale, in parts a sandy and gritty, in others an encrinital and sub- 

 crystalline limestone. 



b. Blotchy grit with much red shale. 



c. Hard, fine-grained calcareous grit, passing downwards into a mottled, 



dingy green, and purple impure limestone with irregular traces of 

 wayboards. 



d. Purple and white limestone, with olotches of red shale. 



