OF THE UPPER CRETACEOUS IN WEST SUFFOLK AND NORFOLK. 545 



The present communication therefore is based npon our joint 

 investigations in the field, checked and confirmed by the results of 

 the borings, by the examination of the fossils collected from the various 

 exposures, and by the study of more than 150 rock-slices under the 

 microscope. 



The mass of evidence thus obtained will naturally be treated under 

 the three heads of (1) stratigraphical evidence, (2) palseontological 

 evidence, (3) microscopical evidence ; and these are supplemented by 

 the chemical analyses which the kindness of Dr. Johnstone enable 

 us to adduce. We desire also to thank Mr. Whitaker for his assis- 

 tance and cooperation in the field, and for his readiness to impart 

 such information as he possessed. 



§ 1. Stratigraphical Evidence. 



For the purposes of description, it will be most convenient to 

 divide our matter into three portions under the following heads : 

 (a) the Gault and the Cambridge Greensand, (b) the Totternhoe 

 Stone and Chalk-marl, (c) the Grey Chalk, Melbourn Eock and 

 associated beds, tracing each division from south to north, and de- 

 scribing the exposures which we observed along the tract occupied 

 by it. 



A. The Gault and Cambridge Greensand. 



On the eastern borders of Cambridgeshire, near Reach, Burwell, 

 and Soham, well-sections prove the thickness of the Gault to be 

 about 100 feet, the information obtained showing a variation 

 between 90 and 110 feet at different places. 



The greater part of the Gault lies below the surface of the Pen, 

 so that little can be seen of it ; but some fourteen or fifteen years 

 ago many Coprolite-pits were open between Reach and Soham, and 

 we quote the following observations from the ' Survey Memoir on 

 the Neighbourhood of Cambridge ' (p. 34) as indicating that the 

 clay which here underlies the Coprolite-bed belongs to a different 

 and probably higher part of the Gault than that on which it rests 

 near Cambridge. The memoir says : — " The phosphate nodules 

 extracted from these pits exhibited different characters from those 

 obtained nearer Cambridge ; there was a much greater proportion of 

 lighter-coloured phosphates, and the fossils which occurred among 

 these had not apparently been subjected to much rolling, but retained 

 their shells in a more perfect state than usual — Terebratulce, Bhyn- 

 chonellw, and Exogyrw being especially common and well pre- 

 served. . . . Amongst the darker nodules there are some which 

 have a greenish exterior, and the whole assemblage has a different 

 aspect from those [of the pits] to the south, as if resulting from 

 the erosion of differently constituted beds in the Gault." 



It is also mentioned that at one pit near Reach ""a second 

 Coprolite-bed was worked in the mass of the Gault, about 8 feet 

 below that forming the base of the Chalk-marl," the fossils from 

 both beds being mixed in the washed heap. 



