﻿Vol. 64.] THE BALA AND LLANDOVERY EOCKS OF GLYN CEIRIOG. 595 



traversed strata all dipping in the same direction, but along it, 

 nevertheless, the outcrops were shifted neither in the same direction 

 nor for an equal distance. The structure, at first sight, seemed 

 impossible ; but an explanation was found in the fact that the dip 

 varied from 50° to 15° along the fault, and in the supposition that 

 the movement of the fault was not vertical, but in a direction that 

 lay between those inclinations. The varying effect upon the 

 outcrops necessarily followed, as might be made apparent by 

 drawing a section of curving beds, and sliding over it a tracing 

 of the drawing, in the direction in which the fault was supposed to 

 have moved. 



Dr. Geoom said, in reply to Mr. Lomas's communication, that the 

 Pandy Ashes were hardly such as could have been derived from 

 the brecciation of igneous rocks, more particularly from intrusive 

 masses. In places true bedding, and even false bedding, was 

 clear ; and the most compact rocks in the heart of the Craig-y- 

 Pandy Ash showed typical ' bogen '-structure. 



Mr. Lake said that, in comparing the fauna of the Bryn Beds 

 with that of the Sleddale Group, the Authors had removed, so far 

 as was possible, from Dr. Marr's list the species that occurred only in 

 the Keisley Limestone. Yet, even then, the Sleddale Group appeared 

 to contain forms that belonged to a higher horizon than the Bryn 

 Beds. As, however, the top of the Bryn Beds was cut out by the 

 Dolhir Pault, this difference was partly explained. The Authors 

 had considered the remarkable fact that a break occurred at the 

 base of the Ashgillian Series in South Wales, as well as in the Glyn 

 Valley. Nevertheless, they were convinced that in the latter area 

 the break was due, in part at least, to a fault. 



