Appendix

Abstract

Although, the particular section described by Mr. Durham has not been examined by me, I have had considerable opportunities of making myself acquainted with the general characters and relations of the igneous rocks of the district where it is exposed. In the year 1876, I spent some months in examining the volcanic rocks of Angus and Fife, under the guidance of the late Sir Charles Lyell, who had such an intimate acquaintance with the geology of the district; and the general conclusions at which I arrived with regard to the relations and ages of the different types of igneous rocks in that area correspond very closely with the views which Mr. Durham has enunciated in the foregoing paper. Among the rocks which Mr. Durham has from time to time sent me for determination, there are several which, from the remarkable state of their preservation and the light which they seem to throw upon some very important petrological problems, appear to me to be worthy of detailed description. I am greatly indebted to the author of the paper, not only for the loan of his own collection of rock-sections, but for the readiness with which he has supplied me with ample materials for further study. Three of the rocks referred to in this paper are particularly interesting in their characters, and may be regarded as noteworthy additions to British petrography. The remarkably fresh rock of Northfield (see Plate XIII. fig. 1) has a specific gravity of 2·68. It is a very