410 CRETACEOUS, 



843 feet of Chalk.' Near Mildenhall a bed of red marly chalk has 

 been observed in the Lower Chalk. - 



CAMBRIDGESHIRE. 



The divisions of the Chalk have been previously noted. (See 

 p. 402.) The so-called 'Cambridge Upper Greensand ' consists 

 of greenish chalky clay passing down into marl with glauconitic 

 grains, from eight inches to one foot thick, and containing 

 scattered phosphatic nodules (coprolites), and phosphatized fossils. 

 The pits show sometimes twelve or fifteen feet of Chalk Marl 

 above, while an eroded surface of the Gault is exposed beneath. 



This phosphatic deposit is particularly rich in vertebrate remains, 

 including a Bird discovered in 1858 by Lucas Barrett, and named 

 Enaliorjiis Barretti, and another species, E. Sedgivicki ; many 

 Reptiles, Ichthyosaurus campylodon, Phsiosaurus, and the Dino- 

 saurian AcanihophoUs (also found in the Chalk Marl of Folkestone) ; 

 likewise many Fish-remains, Otodus appendicidatus, Larnna stibulata, 

 L. gracilis, etc. Among Foraminifera a large form Parkeria is met 

 with. Many Sponges occur. The Mollusca include Ammonites, 

 Scaphites Mcriani, Inoceramus sulcatus, etc. ; and the Brachiopoda 

 include Terebratula hiplicata, RhynchoncUa sulcata, etc. Many 

 species are Chalk Marl fossils, a notable form being the Hippurite, 

 Radiolites Moretoni. 



The Rev. O. Fisher has observed that all the derived specimens (phosphates, 

 etc.) have Plica tichr attached to them, showing that, whatever they were originally, 

 they were hard bodies when they lay at the bottom of the Chalk ocean. Many of 

 them are broken ; and the Plicalulce may frequently be seen to be attached to the 

 broken surfaces.^ The species was named Plicatula sigillina by Dr. S. P. Wood- 

 ward.'' The coprolites are mostly black or deep brown in colour, while their 

 surfaces are pitted, corrugated, or wrinkled : these black coprolites are distinct 

 from the " red" coprolites of the Lower Greensand. Mr. Jukes-Browne observes 

 that the 'coprolites,' fossils, and green grains which it contains have been mainly 

 derived from the denudation of the Upper Gault ; and he considers the bed 

 to belong to the base of the Chalk Marl, the Upper Greensand being absent.* 

 Hence it is probably homotaxial with the so-called Chloritic Marl of the south- 

 west of England. 



The origin of the phosphatic nodules, miscalled ' Coprolites ' (see p. 104), is a 

 subject that has been much discussed. Phosphate of lime, as pointed out by Prof. 

 Bonney, is present in small quantities in the sea, in several rivers, and in numerous 

 mineral springs ; it is found in many plant and animal remains ; and in the form of 

 Apatite it is met with in many rocks. He considers that the phosphatic nodules 

 are due to concretionary action, and have been formed by segregation out of mud 

 saturated with phosphate of lime. "^ At the same time the deposition of the phosphatic 

 matter has been determined by animal substances, for the bones and teeth, and 



1 Geol. Stowmarket, by W. Whitaker, F. J. Bennett, and J. H. Blake (Geol. 

 Survey), p. 19. 



'^ Jukes- Browne, Brit. Assoc. 1S86. 



^ Q. J. xxix. 52. 



* G. Mag. 1864, p. 112. 



^ Q. J. xxxi. 256, 272 ; Seeley, Ann. Nat. Hist. 1S61, 1S65, Q. J. xxxii. 496 ; 

 H. G. Fordham, P. Geol. Assoc, iv. 150. 



^ Cambridgeshire Geology, p. 30. 



