On the Correlation of the Upper Jurassic Rocks of England with those of the Continent.—Part I. The Paris Basin

In former papers on the Portland Rocks, the Kimmeridge Clay†, and the Corallian Rocks‡, as developed in our own country, it has been pointed out that, while the normal deposits of the period commencing with the Oxford Clay and continuing to the close of the Jurassic era were essentially argillaceous, the uniformity has been broken by certain episodes which have resulted in the formation of distinct kinds of rocks, but that, in spite of these episodes, there is a continuousness both in the physical and biological features, uniting the whole into one great group, to which the term Upper Jurassic is appropriated. The present study ought therefore, logically, to include a correlation of the Oxford-Clay series; but though the upper portions of that series come to be incidentally examined, the far wider range and greater constancy of the lower portion would render its examination a more arduous and less interesting task; and it is found convenient to have for base a thick mass of clay, which may almost everywhere be recognized, however much the upper part may be encroached upon lithologically by the various preludes to the Corallian series. In point of fact, the rocks hitherto called Corallian in England comprise much that is placed in the Oxfordian by the French geologists; and our correlation is therefore only stopped when the rocks universally called Oxfordian are reached. The Upper Jurassic rocks of France lie in two distinct areas.The more northern is that which is drained by the Seine and the