256 A. J. JUKES-BROWNE ON THE RELATIONS OF 



18. On the Eelations of the Cambridge Gattlt and Greensand. By 

 A. J. Jukes-Browne, Esq., B.A., F.G.S., of the Geological Sur- 

 vey of England. (Head January 13, 1875.) 



[Plates XIV. & XV.] 



Contents. 

 Introduction. 

 Part I. — Stratigraphical Eelations. 



1. The Gault and Chalk-marl in Cambridgeshire. 



2. The Gault and Chalk-marl in Bedfordshire. 



3. The Gault and Upper Greensand in Buckinghamshire. 



4. The Upper Gault in Bucks and Bedfordshire. 



5. The Gault and Greensand of the Weald. 



6. Conclusions from Stratigraphical Evidence. 



Part II. — Palseontological Eelations. 



1. Natural Division of the Cambridge Fauna. 



2. Further Analysis of the Fauna. 



3. Conclusions from Palseontological Evidence. 



4. Eemarks on the Synonymy of eertain Species. 



5. List of the Cambridge Fossils, and Tables of Eange. 



Introduction. — I cannot do better than preface the following obser- 

 vations 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 

 palaeontological 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 remarks the present communication 

 has for its main objects : — 



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 



* " Continental Geology," Geol. Mag. vol. vi. p. 259. 



