The Zonal Position of the Elsworth Rock and its Alleged Equivalent at Upware

Abstract

(1) The Elsworth Rock of Elsworth and St. Ives is a condensed deposit belonging to the plicatilis zone.(2) There is no evidence that it contains any ammonites derived from earlier zones. Statements that it does are based on misidentifications.(3) The Elsworth Rock at Elsworth overlies at least 8½ feet of ironshot clays with thin bands and nodules of limestone, the clays containing abundant ammonites of the cordatus zone and no others.(4) The so-called Elsworth Rock at Upware is the equivalent of the ironshot cordatus zone developed below the Elsworth Rock at Elsworth.(5) The true Elsworth Rock (plicatilis zone) is represented at Upware by the Coralline Oolite and Lower Coral Rag.(6) For convenience in stratigraphical nomenclature it is desirable to group together the condensed ironshot cordatus and plicatilis beds of Elsworth as the Elsworth Series.(7) The Elsworth Series, as defined in 6, corresponds with the Oolithe ferrugineuse and the greater part of the Oolithe de Trouville on the Normandy coast. At Trouville the plicatilis zone to some extent combines the developments at Elsworth and Upware.(8) The ironshot cordatus zone was proved in the Upware well to rest directly upon normal clays of the mariae zone, and the same zone was proved in the vale below Elsworth in the Fen Stanton brewery boring.I am greatly indebted to Mr. E. E. L. Dixon and Mr. A. G. Brighton for criticisms and suggestions, and especially to Mr. Brighton for the trouble he has taken in sending me all the fossils on loan and supplying the relevant information.