226 Chloritic and Chalk Marl. 



of all the British formations. From west to east it 

 stretches from the neighbourhood of Beaminster in 

 Dorsetshire, to Beachy Head and the North Foreland, 

 and passing beneath the Eocene formations of the Hamp- 

 shire and London basins it spreads northward to Speeton, 

 in Yorkshire. 



The Chloritic Marl indicates a passage from the 

 Upper Grreensand into the Chalk. It consists of a 

 chalky base specked with green grains, and varies from 

 a few inches to a few feet in thickness. It is highly 

 fossiliferous, abounding in Ammonites, Nautili (N. 

 Icevigata), and a small Scaphite (S. ccqualis\ besides 

 Oysters, Trigonias, Holaster, &c., and many other Echi- 

 nodermata. 



The Chalk Marl, which lies above the Chloritic 

 Marl when both are present, is merely chalk with a 

 slight admixture of argillaceous matter, and with its pre- 

 decessor by no means deserves to be considered as a sepa- 

 rate formation. The whole, therefore, may be massed as 

 The Chalk. It consists of a soft white limestone, 

 generally much jointed where exposed in quarries, and 

 but for lines of flints, the bedding would often be 

 scarcely distinguishable. On minute examination with 

 the microscope, much of the Chalk is found to consist of 

 the shells of Foraminifera, Diatomacese, spiculse and 

 other remains of Sponges, Polyzoa, and shells, highly 

 comminuted. Somewhat similar deposits are now 

 forming in the open Atlantic at great depths, chiefly of 

 Foraminifera of the genus Grlobigerina, Polycystina and 

 Diatomacese, and spiculse of Sponges. In the Pacific, 

 also, from Java to the Low Archipelago, over an area of 

 about 4,000 miles in length, all the deep-sea deposits are 

 of fine, white, calcareous mud, like unconsolidated chalk. 

 In its thickest development in England the Chalk is 



