On the Physical Structure and Succesion of some of the Lower Palæozioc Rocks of North Wales and part of Shropshire

Abstract

The Sections to which this notice refers are on a scale of 6 inches to a mile, vertically and horizontally. Section No. 1 passes from Mochras Island in Cardigan Bay, over Cader Idris, Radnor Forest, and Hanter Hill, to the Old Red Sandstone near Fern Hall, south of Kington, Herefordshire. It is about 65 miles in length. No. 2 commencing at Llanfair-is-gaer, Menai Straits, passes over Snowdon, Moe]-wyn, Gors-goch (near Trawsfynydd), Aran Mowddwy, and Newtown, Montgomeryshire, and the Upper Silurian rocks and Old Red Sandstone of Clun Forest, Wigmore Valley, &c., near Ludlow. It is 90 miles in length. No. 3 passes across the Shelve and Longmynd country to the Brown Clee Hills*. These Sections were constructed by Messrs. Aveline, Selwyn, Bristow, and Ramsay; and the mapping of the county to which they refer was executed by them and Mr. Jukes. Sections Nos. 1 & 2.—The oldest rocks crossed by Sections Nos. 1 & 2 lie at the base of the Merioneth anticlinal of Professor Sedgwick. They are the Barmouth and Harlech sandstones, which are here and there interstratified with beds of purple slate. Their base is not exposed, and the lowest beds that rise in the centre of the area are from 6000 to 7000 feet beneath the base of the Lingula flags. In places they are pierced by numerous greenstone dykes, a few of which are magnetic. No fossils have heretofore been found in them. These and their equivalents are the rocks coloured as “Cambrian” by the Geological