The Geology of the Country around Pwllheli, Llanbedrog and Madryn, South-West Carnarvonshire

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Abstract
A number of papers have been published in recent years dealing with the geology of the southern part of the Lleyn peninsula. Mr. T. C. Nicholas in 1915 described the eastern horn, known as St. Tudwal's peninsula; papers by myself (1902, 1913, 1925, 1928, 1932) dealt with the western coast from Bardsey Island to Nevin and inland to Rhiw and Sarn, and one in 1930 by Dr. Heard and myself with the Bodfean tract. The purpose of the present communication is to describe the remaining area (about 42 square miles), which extends from Porth Neigwl (or Hell's Mouth) northward to Bodfean and eastward to the coast between Abersoch and Pwllheli, and thence to the neighbourhood of Four Crosses. This country is built of Ordovician sediments accompanied by members of the “Bala Volcanic Series” and its associated intrusives. Glacial drift covers large areas, but the igneous rocks often project as prominent ridges and hills, of which the dominant peak is Carn Fadryn, 1217 feet high. The southern part of the area is a plain of thick drift which has filled up the head of the wide-mouthed bay of Porth Neigwl. The western horn of the bay at Rhiw and the eastern horn south of Llanengan are prolonged inland as pre-glacial cliffs and slopes, and the glacial deposits between them, which must have once extended farther south, are being removed by sea-erosion; yet at their truncated southern margin they still extend below sea-level. The Afon Sôch, with its tributary the Afon Horon,

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