On the Lower Cretaceous Beds of the Bas-Boulonnais, with notes on their English Equivalents

Publisher Website
Google Scholar
Abstract
T he following notes are the result of an excursion made, with my colleague Mr. Whitaker, in the summer of 1866, supplemented by two hasty visits by myself later in the same year. To Mr. Whitaker and to M. E. Rigaux, of Boulogne, I am indebted for much assistance. I. G eneral D escription of the D istrict . The Bas-Boulonnais forms the easterly continuation of the English Wealden area, both being bounded alike by a well-defined escarpment of Chalk. The lowest beds exposed in the Weald have been doubtfully referred to the Purbeek formation; but none of undoubted precretaceous age occur therein on the English side of the Channel. In the Bas Boulonnais the major part of the surface is occupied by Lower Secondary and Palæozoic beds, the Lower Cretaceous rocks occupying only a narrow border at the foot of the Chalk escarpment, and capping the hills in the interior. The Chalk falls away from the escarpment with a gentle slope. The Gault generally occupies a slight depression at the base of the Chalk hills; but, from its diminished thickness, the valley thus formed is far less striking than in Kent. The Lower Greensand is too thin to make a constant feature in the district; towards the south and south-east, however, it, togather with the underlying ferruginous sands, forms the range of hills which runs more or less parallel with the Chalk, but without making a well defined escarpment. The hills of the central district, which are capped by ferruginous sands (Wealden), are mostly

This publication has 0 references indexed in Scilit: