The Geological History of the Rivers of East Yorkshire

Abstract

SINCE Jukes, some forty years ago, explained how rivers cut through escarpments, the origin of their valleys has been well understood in a general way. Much, however, remained to be learnt about the development of particular rivers and the changes which have brought about present drainage areas; and these subjects have been so attentively and successfully studied by American geologists, notably by Prof. W. M. Davis, that their methods of interpretation have been followed by several observers in this country. The present work by Mr. Cowper Reed gained the Sedgwick Prize Essay for 1890, and is a capital exposition of the evolution of the rivers in East Yorkshire. After giving a general account of the various formations, he points out that the original “constructional surface” on which the present river system was initiated, was a plain formed by the Chalk and other Upper Cretaceous strata, and was upraised in early Tertiary times and perhaps partially eroded during the uplift. Having a greater elevation in the west, the direct ancestors of the present rivers took rise from the higher grounds and flowed eastwards, the Tees and Esk forming one river, the Swale and Ure flowing also direct to the coast, which formerly extended much further eastward, and the Nidd, Wharfe and Aire uniting and flowing out by the Humber. A long period of subaerial denudation followed the initiation of these consequent streams, there. was a gradual lowering of the area, and there arose the subsequent river Ouse, which captured the Swale and Ure, the Nidd and Wharfe, conducting their waters into the Humber drainage. Towards the close of the Oligocene period, when the area had been nearly reduced to base-level by the formation of an extensive peneplain and the rivers had attained old age, there was considerable upheaval, accompanied by further movements along pre-Cretaceous lines of flexure, especially in the Moorland range of the Jurassic region. The rivers thereby regained youth and activity, their directions were locally modified, and thus were produced some of the main features in the present topography. Further changes, however, led to other modifications; there was depression towards the close of the Pliocene period, and subsequent elevation in Glacial times. With regard to the Boulder Clay the author judiciously remarks that “the land-ice theory appears to offer fewer difficulties than any others and to explain matters more satisfactorily.” In any case large tracts, excepting some of the higher grounds, were buried beneath drift deposits, and the valleys were choked up. When the land had lost its icy mantle, some of these old valleys were revived, hu in other cases the streams followed new courses. The story of all these changes is clearly told by Mr. Reed, and although there is room for difference of opinion in matters of detail, the main results are based on fact; and the essay may be profitably studied by those interested in the origin of our scenery.

The Geological History of the Rivers of East Yorkshire.

By F. R. Cowper Reed Pp. vi + 103. (London: C. J. Clay and Sons, 1901.) Price 4s. net.