206 PKOF. J. E. MAEE ON THE [vol. lxXV, 



Cambridge ' by W. H. Penning & A. J. Jukes-BroAvne, published 

 in 1881 ; and in that memoir will be found references to previous- 

 literature. 



Since the publication of that memoir many details have been, 

 added, especially by the late Prof. T. McKenny Hughes, in a paper 

 on ' The Gravels of East Anglia.' 1 



It is a great pleasure to record the help that I have received from 

 many students past and present, and others, including American, 

 Australian, and Canadian officers who studied in Cambridge during 

 the summer of 1919. The list is so long that I cannot cite the 

 names, though some will be mentioned in the course of the paper. 

 The enthusiasm displayed by these helpers encourages me to hope 

 that in future years a detailed survey of the Pleistocene deposits of 

 the Great Ouse Basin will be undertaken b}^ the students of the 

 Cambridge School of Geology, and I believe that this preliminary 

 paper will be of assistance to them in carrying out further work, 

 though I trust that it will also be useful to workers in other 

 districts. 



I desire also to record my indebtedness to the late Mr. Clement 

 lleid, F.P.S., and to Mrs. Eleanor Reid, for determination of plant- 

 remains ; to Mr. A. S. Kennard & Mr. B. B. Woodward, for identi- 

 fying mollusca ; to Mr. M. Burkitt, for help with the implements ; 

 and to Mr. C. E. Gray, for identification of mammalian bones. 

 Mr. Kennard & Mr. Woodward and Mr. Burkitt have been so- 

 good as to furnish Appendices to the paper. 



I would acknowledge the courtesy and help extended by pit- 

 owners and workmen on all occasions. The thanks of Cambridge 

 geologists are specially due to Messrs. Swann for allowing free 

 access to their pits. 



II. The Time-Sequence. 



The Geological Surveyors classified the Pleistocene deposits 

 of the Cam Valley as follows : — 



C Lowest Terrace. 

 Gravels of the Present River-System. ^ Intermediate Terrace. 



( Highest Terrace. 

 Gravels of the Ancient River-System. 



1 shall give reasons for supposing that the gravels referred to the 

 ancient river-system are in part contemporaneous with those assigned 

 to the present river-system, and that the latter contain deposits of 

 very different ages, some having been formed during a period of 

 aggradation, others during one of erosion. In the absence of con- 

 tinuous sections it is usually difficult to ascertain whether the gravel 

 of a higher ' terrace ' reposes upon one at a lower level, or whether 

 the deposits of the latter are banked against those of the former. 

 In the former case, the more elevated gravels are the newer ; in the 

 latter, those at a less elevation. 



In the paper published in the Proceedings of the Cambridge 



1 Cambridge University Press, 1916. 



