580 MESSES. JT7EES-BE0WNE AND W. HILL ON THE LOWEE PART 



chonella plicatilis ; but as the bed is only exposed at three or four 

 localities and is very thin, this paucity of fossils is not surprising. 



The letter B in the Dersingham column means that the species 

 so indicated are quoted from Dr. Barrois's list in his ' Becherches sur 

 le Terrain Cretace superieur/ 



Table Y. — Fossils of the Melbourn Rock and zone of R. Cuvieri. 

























rret 

 stead. 



ford. 



Pn g 

 a — 



ngton. 



O fciD 





nbeatl 



enhall 



o 



bX) 



a 







bJD 

 T3 



o 



■ — ( 

 -i— i 





0) 







o 





m 





w 





& 





i 





Cardiaster pygmaeus, Forbes 









































Echinoconus subrotundus, Mant... 



* 













* 







castanea, Brongn 















































■Sf- 















Terebratula semiglobosa, Sby 





* 



* 













if 



Bhynchoneha Cuvieri, d 'Orb 













* 









Inoceramus mytiloides, Mant. ... 







* 1 ... 



#• 









if 



Ammonites peramplus, Mant 







* 















Cunningtoni ?, Sharpe 







* 















The fossils on this zone, as might be expected from the constancy 

 of its lithological characters, are the same as those which it contains 

 in the Midland and Southern counties. The lower beds of the 

 Melbourn Bock are, as usual, without fossils, but the upper beds and 

 the shelly chalk above abound in Rhynchonella Cuvieri and Ino- 

 ceramus mytiloides, while the echinid Echinoconus subrotundus is 

 hardly less common above the Bock. 



§ 3. Beview of the minute Steucture of the Bees desceibed 



in this Paper. 



Gault. — The examination of specimens from various horizons of 

 this formation, from Chatham Well-boring, Streatham Well, Arlesey, 

 Tring, &c, shows them to consist in great part of inorganic material 

 in an exceedingly fine state of division ; on this acid has no effect, and 

 it is negative under crossed nicols. An inconsiderable portion can 

 be recognized as very fine quartz-sand, mica, grains of glauconite, 

 and fragments of a fibrous material, probably of felspathic origin. 

 Fragments of shell, Foraminferal tests, and minute atoms which 

 appear to be calcareous and disappear after acid, are present in 

 varying proportions ; but the deposit, as a whole, may be spoken of as 

 inorganic. 



The material composing the Upper Greensand which overlies the 

 Gault in Buckinghamshire is in a much coarser condition, and the 



