IV.—The Application of Petrological and Quantitative Methods to Stratigraphy

Abstract

Although detrital mineral work is as yet in its infancy, sufficient has been accomplished to show that we may look to it with success for indications of changes of drainage direction, evidences of denudation by reversal of the order of respective mineral assemblages from a sequence of rocks, and generally for information regarding details of palæogeography. Professor A. de Lapparent referred to Professor L. Cayeux's work as proving the proximity of land, composed of primary rocks, to Lille in Landénian times. Dr. H. H. Thomas was able to demonstrate the change in source, and therefore in direction of drainage, of the river-borne heavy minerals in the Bunter sandstones of South Devon, the occurrence of garnets and staurolite being especially significant. Dr. T. O. Bosworth, in some preliminary work upon the detrital minerals of the Carboniferous Sandstone of the Midland Valley of Scotland, was led to the conclusion, partly by the respective presence and absence of garnets, that the beds could be divided into a series of great lenticular masses of sediment introduced from directions varying from north and north-west to north-east, east, and south. Mr. W. R. Smellie has discussed in rather more detail the origin of the minerals in the Upper Red Barren Measures of the Glasgow Basin, the drainage having been from the west or north-west.