The Toadstones of Derbyshire: their Field-Relations and Petrography

Abstract

I. Introduction. In June 1894 I read a paper before this Society, ‘On the Microscopical Structure of the Carboniferous Dolerites & Tufts of Derbyshire’ Quart. Journ. Geol. See. vol. 1, pp. 603-44 & pls. xxiv-xxv. At that time I had made no attempt to establish the relations in the field between the igneous rocks and the limestones in which, they occurred. During the interval which elapsed between the acceptance of my paper by the Council of the Society and the reading of it, I had the pleasure of taking Sir Archibald Geikie over some typical parts of the district. He pointed out that some of the toadstones were contemporaneous with the limestone, others intrusive, and others represented the vents through which the volcanic material was brought to the surface; and that, in order to arrive at the history of the toadstones, careful re-mapping of the whole district would be necessary. In 1897, in his ‘Ancient Volcanoes of Great Britain’ vol. ii, p. 12, Sir Archibald expressed the opinion that ‘the number of successive platforms on which igneous materials appear will never be satisfactorily determined until the stratigraphy of the Derbyshire Carboniferous Limestone is worked out in detail. When the successive members of this great calcareous formation have been identified by lithological and palæontological characters over the whole district, it will be easy to allocate each outcrop of toadstone to its true geological horizon.’ Since November 1894, I have mapped the toadstones on the 6-inch Ordnance maps and