A Metamorphosed Nodular Shale previously described as a “Spotted” Metamorphic Rock

Abstract

In the Geological Magazine for 1895 and again in 1898 W. M. Hutchings gave a petrological description of a shale, metamorphosed by the Whin Sill of Teesdale, which showed three unusual features. Scattered irregularly through the hardened shale were large nodules about the size of a pea which Hutchings considered to be the results of the metamorphism, in fact to be unusually well-developed “spots”. The second peculiarity was that both matrix and nodules contained considerable amounts of an isotropic material which was maintained to be the result of incomplete crystallization of a dense solution formed from the constituents of the shale during metamorphism. Finally, the detrital quartz grains of the shale were found to be extensively replaced by muscovite or more rarely other minerals. A reexamination has been made of the rock and also, by the courtesy of Professor G. Hickling, of Armstrong College, Newcastle-upon-Tyne, of certain of Hutchings's slices. In this note it is not intended to redescribe what has been ably described in Hutchings's papers, but as briefly as possible to make two corrections of Hutchings's conclusions.