The Islay Anticline (Inner Hebrides)

Abstract

In a paper which I had the honour of reading before this Society on November 19th, 1879, entitled “On Concretionary Patches and Fragments of other Rocks contained in Granite,” I called attention to the fact that a certain class of such inclusions, usually more or less ovoid in form and resembling imbedded pebbles, are essentially composed of a fine-grained variety of the granite in which they are severally enclosed. The proportion of dark-coloured mica in these patches is almost invariably greater than in the rock in which they occur, and imparts to them a darker colour than that of the general mass. It was further observed, when sections made through both pebble-like inclusions and the enclosing granite are examined under the microscope, that along their line of contact minute crystals are found to extend from the one into the other. These rounded inclusions sometimes enclose a second similar nodule, differing from the first either in colour or in fineness of grain only.