1853.] SHARPE SANDS AND GRAVELS OF FARRINGDON. 183 



that curious deposit* has been of the greatest assistance to me. The 

 Tourtia appears to be a gravel beach of the age of the Upper green 

 sand, yet it contains some species common to the Upper Chalk ; and 

 the grey marly chalk which covers it also contains some mixture of 

 species of the Upper with those of the Lower chalk. It is probably 

 owing to the littoral origin of both deposits, that we find so strong 

 a connection between the Tourtia and the Farringdon gravels. 



Throwing together the Upper green sand and the Tourtia, and 

 adding thereto the species indicated in the ' Paleontologie Fran^aise' 

 from the Craie Chloritee^ all of which, for convenience, we will call 

 Upper green sand, we have 50 species common to these and the 

 Farringdon gravels, of which 13 species are also found in beds above 

 the Upper green sand, 3 in beds below it, and 1 in beds both above 

 and below it ; leaving .'-{3 species hitherto thought peculiar to the 

 Upper green sand, and now found at Farringdon, These belong 

 principally to the Amorphozoa, Bryozoa, Monomyaria, and Brachio- 

 poda ; but the most striking resemblance is of the Sponges of Far- 

 ringdon with those of the Upper green sand of Essen on the Ruhr, 

 and of the Brachiopoda with those of the Tourtia of Belgium. 



But if instead of comparing the fauna of Farringdon with that of 

 foreign localities, we look to the Upper green sand of its immediate 

 neighbourhood, we shall find very little resemblance. The Upper 

 green sand of Berkshire contains few fossils, and of these very few 

 are found at Farringdon : a few more Farringdon species are found 

 in the uppermost bed of the Upper green sand at Warminster, but 

 there is no spot in England where the Upper green sand aifords an 

 assemblage of species at all similar to those of Farringdon. 



The Lower chalk bears very little comparison with the Farringdon 

 gravels in its organic contents : only 1 1 of the Farringdon species are 

 known in that deposit, and of these 3 are also found below the Lower 

 chalk, and 4 both above and below it. 



The Upper chalk, on the contrary, contains 32 Farringdon spe- 

 cies, of which 4 are also found in lower formations, 2 also in the 

 Maestricht sands, and 2 both in the Maestricht sands and beds below 

 the white chalk. More than half of the ('halk species found at Far- 

 ringdon are Bryozoa. 



The Maestricht sands contain 1 2 species found at Farringdon, of 

 which 10 are also found in lower beds ; of these latter 5 are in the 

 Upper green sand, but not in the Chalk. Unfortunately there is no 

 good list of the mollusca of the Maestricht beds, and the collections 

 in this country of Maestricht fossils are very poor, so that I have less 

 opportunity of comparison with the species of this bed than with those 

 of the lower beds of the cretaceous series. 



The Terrain Banien of M. d'Orbigny comprises several deposits, 

 which are considered by him to belong to a place in the cretaceous 

 series above the Chalk ; these are the coralline limestone of Faxoe and 

 various deposits of pisolitic limestone near Paris. This has led to 

 some controversy among the French geologists, many of whom regard 

 the pisohtic limestone as a Tertiary formation. Without entering at 

 * d'Arcliiac, Meiaoirs of the Geol. Soc. of France, 2iid Series, vol. ii. 



