108 Dr. FiTTON on the Strata below the Chalk. 



thick, at the top of the hill on which the Tower No. 3. is placed*; and in this 

 place the stratum consists of a soft marly sand, traversed in every direction 

 by stem-like cylinders, which have within them cores of darker green matter. 

 It also contains some irregular masses of a bright brown or orange hue ; 

 but the greater part is composed of grey calcareous marl, like the lowest 

 chalk, so thickly interspersed with green particles as to exhibit only their 

 colour. 



The fossils which I found in this stratum were few in number, and in- 

 distinct : the only species that could be ascertained was the Pecten orbicu- 

 larisli, one of the characteristic shells of the lower chalk and upper green- 

 sand in Hampshire and Western Sussex. 



(10.) The green matter, which abounds in this stratum near Wissant, on the 

 opposite coast of Prance, has been examined by M. Berthier;}; ; who found it to 

 consist principally of silica and protoxide of iron, with ten per cent, of potash. 

 For the purpose of comparing the green-sands of different places and forma- 

 tions, my friend Dr. Turner, Professor of Chemistry in the London Univer- 

 sity, was good enough to examine some specimens from the upper and lower 

 green-sands of Folkstone, of the Vale of Wardour, and the Boulonnois, and 

 also particles of the same kind which abound in the sand and concretions 

 beneath the Portland stone, in the Boulonnois, and in England. I subjoin 

 the result of this examination §, whence it appears that in all these cases the 



* See Plate VIII. and the Section, Plate Xa. No. 1. 



•)• Mineral Conchology, tab. 186. 



J Cuvier and Brongniart, Environs de Paris, 2nd edit. 1822, p. 249. See also Annales des 

 Mines, iv. 1819, p. 623.; and v. 1820, p. 197. 



§ The following passages are transcribed from the notes with which Dr. Turner has favoured 

 me upon this subject. 



" The colouring matter of green-sand sometimes appears in the rock of its ordinary green tint, 

 and sometimes in grains of so deep a green that tliey seem black. The former generally occurs in 

 sand, or where the sandstone is porous, and in this state an ochreous appearance is often observed, 

 due to the green particles being partially decomposed, and their iron having passed into a higher 

 state of oxidation ; whereas the black-looking grains are met with in highly calcareous sand- 

 stone, where the texture is too firm to admit of the percolation of water. From either kind of rock 

 the green matter may be obtained by washing with water and subsidence, since the colouring matter 

 subsides less readily than grains of quartz, and more readily than calcareous and argillaceous sub- 

 stances. For the purpose of analysis it is best procured from tliose calcareous sandstones where 

 the cement predominates, as in the neighbourhood of Hythe and Folkstone in Kent. On reducing 

 such samples to powder, washing away the finer particles with pure water, and separating any 

 adhering carbonates by dilute muriatic acid, the colouring matter is left, mixed only with small 

 grains of quartz. It then always appears in the form of earthy particles of a deep green tint. 



" The green matter, when not previously weathered, is very feebly attacked by concentrated acids, 



