On the Corallian Rocks of England

Abstract

I ntroduction W hatever may be the value of the grounds on which the ordinary line of separation between the “Middle” and “Upper” Oolites is drawn, there can be no denying that from the Oxford to the Kimmeridge Clays, in some parts of England, we have one continuous deposit, which, from a physical point of view, has been aptly termed a great “pelolithic” formation. During the period when this was being quietly laid down, at a quicker or slower rate, in these areas, other portions of the same great region were at various times subject to alterations of the physical conditions, in consequence of which the deposits were changed in character; they became Grits or Limestones, and supported coral reefs, with their accompanying Oolites. The very fact of these changes being local—a fact proved as much by the discontinuous as by the variable nature of the deposits—prevents our assuming that they were all contemporaneous, even in a large sense, as has been done by those who have used the term Corallian, as indicative of a period, for all or any of the coral deposits that have been formed between the commencement of the Oxfordian and the close of the Kimmeridgian epoch. In England, however, these rocks, originally called “Coral Rag” by Smith, from their development in that form in the area studied by him, have been divided into Upper Calcareous Grit, Coralline Oolite , and Lower Calcareous Grit , the classification being originally derived from Yorkshire; and it has been too hastily assumed that rocks