254 



GEOLOGY OF THE ISLE OF WIGHT. 



Phosphoric Acid, etc., in Nodules and Casts of Shells, in the 

 Chloritic Marl, St. Catherine'' s Doions. 



* Good Cambridge coprolites contain about 26 per cent, of phosphoric acid. 



Chalk. 

 A very thin, but well-marked band of nodular chalk, known as 

 the Chalk Rock, runs through the whole of the central range of the 

 Island, as described on pp. 75-89. The nodules are slightly phos- 

 phatic as shown by the following analysis, made by M. Duvillier for 

 M. Barrois.^ 



Nodules from the Chalk-rock of Shalcombe Down. 



Insoluble matter, clay 

 Soluble silica 

 Oxide of iron 

 Phosphate of lime - 

 Carbonate of lime 



Soluble Silica. 

 The Upper Greensand of the UnderclifF was examined by 

 Messrs. "Way and Paine for the purpose of comparing it with a 

 bed of the same age in the neighbourhood of Farnham, in which 

 silica in the soluble form existed in large proportions. f^^ey 

 found however that the Upper Greensand of the Isle of Wight 

 was comparatively poor in this form of silica, as shown by the 

 following table. it should be stated that the silica, which of 

 course formed one of the largest constituents of the sandstones, 

 occurred as quartz, &c, in the insoluble form, 



* Craie de I'lle de Wight, 1875, p, 19. 



