The lithostratigraphical correlation of the uppermost Rhaetic and lowermost Liassic strata of the W Somerset and Glamorgan areas

Abstract

Summary Richardson's (1911) detailed correlations of the Upper Rhaetic and Lower Lias strata of W Somerset are in need of revision; he wrongly identified the basal Langport Bed as the Cotham Marble at Blue Anchor and Lilstock. Likewise, his correlations of the Upper Rhaetic and Lower Lias strata between W Somerset and Glamorgan are erroneous; the lower parts of his Glamorgan Langport Beds were equated with the upper part of his W Somerset Cotham Beds. The greater part of the W Somerset Watchet Beds are, in the hand specimen, lithologically similar to Liassic shales and not to the White Lias ‘marly’ beds of Lavernock as he stated. The matter is important because the W Somerset coast is the recommended type area for the base of the Jurassic System, and Richardson&s classification of the strata is taken as the starting point for fixing this horizon.