144 UPPER, OR FLINTY CHALK. 



Silex - 98- Oxide of iron - - 0-25 



Lime - 0-5 Water - - - 1- 



Alumine - 0-25 



It is infusible, but upon being submitted to a great heat becomes 

 white, and opaque. By exposure to the atmosphere, it undergoes con- 

 siderable change, and assumes a yellow or ferruginous colour, an appear- 

 ance commonly exhibited by the flints of our ploughed lands. When 

 in contact with ochraceous clay, or sand containing iron, it frequently 

 attains a dark carnelian colour externally, the interior being of a lighter 

 shade ; of tliis kind, numerous beds occur in the parish of Barcombe. 



Flints so commonly enclose the remains of sponges, alcyonia, and other 

 zoophytes, that some geologists are of opinion that the nucleus of every 

 nodule, was originally an organic body *. That this has been the case in 

 most instances is very evident ; and in Sussex, there are comparatively but 

 few flints, that do not possess traces of zoophytical organization. These 

 nodules oftentimes exliibit not only the outline of the original zoophyte, 

 but also its internal structure, preserved in the most delicate and beautiful 

 manner that can be conceived. In some examples the zoophyte has 

 undergone decomposition, and the space it occupied been partially filled 

 with an infiltration of agate, chalcedony, and crystallized quartz. 



Although even in the present advanced state of chemical science, we 

 are unacquainted with the process by which silex may be dissolved in water, 

 yet that its solution was formerly effected by natural causes on a very ex- 

 tensive scale, the sihceous nodules, whose history is the subject of these 

 remarks, afford the most conclusive evidence. At the present moment, 

 nature in her secret laboratories is still carrying on a modification of the 

 same operations ; of which we have remarkable instances in the boiling 

 springs of the Geyser, in Iceland -f, and of Carlsbad, in Bohemia :]:. Nor 



* " So far as my observation extends, zoophytes appear universally to have formed the 

 nuclei of nodulated and coated flints." To'wnsend's Character of Moses. 



-f The depositions of siliceous tufa, or chalcedony, formed by the boiling springs of the 

 Geyser, in Iceland, are well known; these waters contain 31 -SS, of silex per gallon. Vide 

 Travels in Iceland, by Sir George Stewart Mackenzie, Bart. 4to. Edinbui'gh, p. 389- 



I According to the experiments of Klaproth, the spring at Carlsbad contains 25 grains of 

 silex in 1000 cubic inches of water. 



