THE CAMBRIDGE GAULT AND GREENSAND. 279 



Were it not for the number of species and paucity of individuals, 

 their presence might be accounted for by supposing their range to 

 have here extended into higher beds. Three other species of the 

 Folkestone Lower Gault appear to have so extended their range, 

 viz. Ammonites auritus, Nucula bivirgata, and Trochocyathus angu- 

 latus ; but they are comparatively abundant fossils at Cambridge, 

 while it is the rarity of the species under consideration which 

 argues their actual derivation from Lower. Gault, a conclusion 

 which entirely agrees with the evidence obtained from the strata 

 themselves ; for, as before mentioned, the Lower Gault is worked for 

 coprolites near Campton, in Bedfordshire. Here the well was sunk 

 28 feet, which, allowing 8 feet for Lower Greensand, agreed very 

 well with the information obtained at Shillington about a coprolite 

 seam 180 feet down. By the kindness of the manager, Mr. T. W. 

 Balls, I obtained the following fossils from the washed heap : — 



Belernnites ultimus, 2? Orb. 



attenuates, Sow. 



Ammonites lautus, Sow. 



auritus ?, Sow. 



interruptus, Brong. 



Beudanti, Brong. 



Hamites rotundus, Sow. 



Natica gaultina, If Orb. 

 Rostellaria elongata, Sow. 

 Plicatula pectinoides, Sow. 

 Inoceramus concentricus, Park. 



(large variety). 



Nucula pectinata, Sow. 

 Terebratula biplicata, Sow. 



The last of these (Terebratula biplicata) has never before been 

 found at so low an horizon ; I obtained it myself, however, on the 

 spot. Many of the nodules were of large size, and the whole assem- 

 blage is similar to that in beds I. and II. in the Folkestone section. 



Again, throughout the Cambridge Gault bands of coprolites are 

 not uncommon. Mr. Bonney has kindly furnished me with a note 

 on their occurrence in the great Gault pit at Barnwell : in the 

 upper part he found irregular layers and scattered nodules of a pale 

 buff colour externally, but dark inside (among them he noted speci- 

 mens of JRhabdospongia, Bonneyia, and Hylospongia) ; about 20 feet 

 down he found a thicker seam of larger nodules, and below this 

 more coprolites scattered sparsely; other fossils are rare in the 

 Cambridge Gault, but I have myself obtained Ichthyosaurus (ver- 

 tebrae), Plicatula pectinoides (fairly common), Trochocyathus angu- 

 latus, Hamites, sp., Terebratula biplicata, Nucula pectinata. 



Higher beds might have been more productive, and have furnished 

 some of the fossils now in the Cambridge Greensand, as suggested 

 above. 



The total number of species, excluding Vertebrata, which are at 

 present reckoned in the Cambridge derived fauna is 210 : deducting, 

 therefore, from this number all the species contained in the two pre- 

 ceding lists as only impeding comparison with other faunas, we 

 have 85 remaining, which are at least tolerably common in the 

 vicinity of Cambridge, and 66 of which (or 78 per cent.) are found 

 in the English Gault ; of these, 60 (or 71 per cent.) occur in the Upper 

 Gault of Folkestone and Bucks ; again, 62 out of the 85 (or 73 per 

 cent.) are found in the Vraconnien of Prof. Benevier. If we only 

 except from the original 210 those which are unknown in any other 



