﻿Vol. 64.] BALA AND LLANDOVEEY ROCKS OF GLYN CEIEIOG. 553 



almost universally mistaken for the ' Little Ash ' of Jukes, but the 

 ' Little Ash ' lies at a higher level and is truly an ash. 



Above this intrusive sheet lie some 400 feet of slates with beds 

 of sandstone, which are sometimes very calcareous and contain 

 numerous fossils. The ' Little Ash ' itself is exposed at Pen-y-graig, 

 where it is marked on the 1-inch map of the Geological Survey, 

 but it is not visible at any other point in the valley, and does not 

 appear in the line of the section. 



The Dolhir Eault. — A long strike-fault now cuts off the top 

 of these beds, slanting down the western side of the valley from 

 Pen-y-graig to Dolhir, and up the eastern side, along the foot of a 

 line of low cliffs, towards Pant. Its strike is east and west, and its 

 dip is northwards at 20°. 



Dolhir Beds. — The fault is followed by beds which differ 

 completely in character and in fossils from those below. Im- 

 mediately above the fault they consist of soft shivery slates with 

 nodules of limestone. A little higher the nodules become more 

 abundant, until they form a baud consisting almost entirely of 

 limestone, which has been quarried by the roadside above Dolhir 

 and also on the opposite bank below Plas Einion. The limestone 

 is followed by some 600 feet of slaty beds which continue nearly to 

 the grit above. They again become calcareous as we approach the 

 limestone at the base of the grit, and there appears to be no very 

 definite line of demarcation between the two series. 



Glyn Grit and Limestone. — The Dolhir Beds are overlain, 

 apparently with perfect conformity, by a band which has usually 

 been taken as the equivalent of the Corwen Grit. On the right 

 bank of the Ceiriog the band begins with a crystalline limestone, 

 which is well exposed in two small quarries on the top of Mynydd 

 Pron Prys. In the upper part of the limestone thin siliceous 

 bands begin to appear, and these gradually become increasingly 

 abundant until they form a thick bed of platy sandstone, which may 

 be traced almost uninterruptedly for 3 miles. 



On the west side of the valley the limestone has not yet been 

 detected, but the grit is of very considerable thickness and covers 

 a large part of the hill-slope on the southern side of Want Llafar. 



As we are now by no means certain that either the limestone or 

 the grit is the equivalent of the Corwen Grit, we propose for the 

 present to speak of this band as the Glyn Grit, leaving its 

 relations to the Corwen Grit for future study. 



Pron-Frys Slates. — The grit is followed in Nant Llafar 

 and on the slopes of Mynydd Pron Prys by grey slates with thin 

 siliceous bands, very similar in character to the grey slates that we 

 have described in the neighbourhood of Corwen. At Corwen, 

 however, they seem to be almost unfossiliferous, while near Glyn 



