On the Older Palæozoic (Protozoic) Rocks of North Wales

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Abstract
Introduction: In a paper read before the Geological Society in June, 1843, and intituled, “ An Outline of the Geological Structure of North Wales,” the author gave a description of those stratified rocks in the northern counties of the principality which are of anterior date to the mountain limestone. Those rocks he separated into the following three principal groups:— 1. Chlorite-slate and mica-slate. These form a band along the north-western side of the promontory of Carnarvonshire from Porth Dilleyn to Bardsea island. 2. Greywacke and roofing slate, often containing calcareous bands, and alternating with Plutonic rocks of cotemporaneous formation: and these rocks the author terms, in his present paper, the Protozoic , group. They extend in an east and west direction, from the borders of Shropshire to the western coast of Carnarvonshire; and their north-western boundary, from the confines of Shropshire to Yspytty Evan, coincides nearly with the Holyhead road; and from Yspytty Evan to Conway, with the Conway river. 3. An overlying and sometimes unconformable deposit of flagstone, &c., coterminous along the Holyhead road and Conway river with the last-mentioned principal group; but bounded towards the north-west by an overlying range of mountain limestone.

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