The Basic Intrusive Rocks Associated with the Cambrian Inlier Near Malvern

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Abstract
I. Introduction T he rocks to be described occur as minor intrusions in the Cambrian strata which are exposed in a small elongated inlier situated on the western flank of the Malvern Hills, east of Eastnor village, Herefordshire (Ordnance Survey 6-inch sheet, Hereford XLII NW.). Their general petrographic features have been described by T. T. Groom (1899, pl. xiii; 1901, p. 158), whose work is now supplemented by the results of a chemical and petrological re-examination of the rocks. Groom (loc. cit.) showed that the intrusives invade the Cambrian strata but not the Silurian. He recognized three main types: (1) an amphibole-bearing andesitic type (probably camptonitic), forming dykes, sills, and bosses; (2) porphyritic olivine-basalts, forming sills and small laccolites, and (3) olivine-diabases, forming sills with porphyritic margins. These were found at five localities only in the grey Bronsil Shales. Further descriptive reference to these rocks is confined to one instance, by Groom himself (1910, p. 704). II. Petrography With some modification of nomenclature the abovementioned three-fold grouping is retained in the following description of the main rock-types. The Splitic Andesities (Group A) These are very fine-grained purplish grey rocks, porphyritic and sometimes trachytic in texture, corresponding in general with Groom's “amphibole-bearing andesitic type”. They are free from vesicles, and occur as (1) dykes in the Hollybush Sandstone north-north-west of Ragged Stone Hill, and (2) bosses or sills in the black shales south-east of Fowlet Farm, and the grey shales south-east of Martins (Fig. 1). In thin section they show a microcrystalline

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