The Origin of the Pillow-Lava near Port Isaac in Cornwall

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Abstract
The volcanic mass which we are about to describe occupies a definite horizon in the Upper Devonian, in the part of North Cornwall lying between Padstow and Bodmin Moor. We propose to confine our remarks to this limited area; for the point with which we deal is merely the mode of origin of this particular eruptive rock. Our views may, or may not, be applicable to other pillow-lavas; but the subject is so beset with difficulties, that we prefer to confine our attention to a limited region, where cliff-sections are exceptionally fine and inland quarries are also clear. We will not deal with the question of correlation, even with neighbouring areas. The volcanic rocks near Port Isaac were noticed by De la Beche in 1839. He mentions the vesicular character of some of them, and suggests that they were contemporaneous with the slates in which they occur. He does not allude to their peculiar structure. In 1848 Nicholas Whitley noticed and figured the peculiar concentric structure, ‘as if it had rolled down a declivity and become partially cooled during its progress, and then consolidated into the rock which it now constitutes; in fact, much like the ends of bales of cloth piled one on another. He speaks of the centre of each circle being generally composed of a nodule of crystallized gypsum, and compares this structure with that of some of the Vesuvian lavas. The petrological characters of these rocks were described in 1878 by J. A. Phillips, who gave

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