COLLECTION, EXAMINATION, ETC. 303 



with water until the required transparency is 

 attained. The sHce is then mounted in Canada 

 balsam and covered with a thin glass. 



It is the rule to find fossil Foraminifera havino- 

 their original shells, but in some cases only their 

 partial remains are found, in the form of casts, 

 usually internal. These are formed by the infilling of 

 the chambers with various mineral substances, such 

 as chalcedony, glauconite, marcasite, calcite, phos- 

 phatite, chalybite, haematite, and limonite. 



The hollow flints, containing the fine white 

 powdery substance sometimes known as 'flint meal,' 

 yield casts of Foraminifera in chalcedony generally 

 in abundance. In many cases not only the casts 

 but actual replacements of the tests are found in this 

 substance, as in the meal deposits in the pot stones 

 (paramoudras) in the Chalk of the North of Ireland. 



The GLAUCONITE casts of foraminiferal shells are 

 found in extraordinary abundance in certain fossili- 

 ferous deposits, as in the Hollybush Sandstone of 

 Shropshire, which is of Cambrian age ; and the 

 Neocomian and Aptian glauconitic sandstones of the 

 Isle of Wight. The greensands of the Lower and 

 Upper Greensand formations in the South of England, 

 the Greensand beds of the Gault and the Cambridge 

 Greensand, and also the Upper Cretaceous Hibernian 

 Greensand of the North of Ireland are all largely 

 composed of these glauconite casts, chiefly of Forami- 

 nifera. In strata of Tertiary age the basement beds 

 of the London Clay, the glauconitic clays of the 

 Bracklesham series, and the Barton beds also yield 



