On the Relations of the Cambridge Gault and Greensand

Abstract

I ntroduction .— I cannot do better than preface the following observations with a few words from the pen of Mr. Davidson in the ‘ Geological Magazine ’ for 1869*. These are :— “Some considerable difference of opinion has been expressed, not only at home, but also on the Continent, as to the real value or position of the well-known Cambridge Greensand or Phosphate-bed. Some consider it to constitute a portion of the Upper Greensand, while others would refer it to the upper portion of the Gault; and, abroad, some geologists constitute a distinct stage, for which the term, Vraconnien is proposed..... It is a point of great importance to determine the exact age of this Cambridge bed; and in making a palæontological comparison there are several points in the case which will call for especial caution; and, as suggested by Mr. Judd, we must in the first place determine whether there are any derived fossils in the bed (so often met with in beds of phosphate nodules).” In accordance with the above 1. To determine the true position of the Cambridge bed in the Cretaceous series. 2. To trace the extent of country along which the formation may be followed. 3. To investigate the origin and age of its organic contents. Before, however, the above-quoted paragraphs had come under my notice, the Cambridge nodule-bed had been for three or four years my especial study, which a residence in Cambridge gave me great opportunities of prosecuting. I wish therefore in the first