Page:A Treatise on Geology, volume 1.djvu/252

 236 is, however, perfectly proved by the regular arrangement of the flint nodules, which are so common in its upper part. No layers of sand (or clay?) occur in any part of its thickr:ess. Joints are not, in general, either numerous or regujar in these formations, nor, excepting geodes and shells of oxides of iron, and the nodules of flint and chert, are concretionary structures common among them

Succession of Strata.—The basin of Europe offers generally the same succession of cretaceous deposits, as in the British islands; but there are local variations of importance. Two formations constitute this system in England and Ireland, which may be thus analysed and described:—

In the north of England the upper green sand is totally deficient; nor is it so distinct from the chalk formation in Kent and Sussex as in Berkshire and Wiltshire. In Yorkshire there is no lower green sand, but in Lincolnshire it is greatly developed, and contains useful calcareous beds. In the north of Ireland the series of cretaceous rocks corresponds nearly to the Englis type, the green sand being called mulatto, but the chalk is generally harder. Round the basin of Paris the series