UPPER CHALK. 
75 
posure to the atmosphere, it undergoes considerable 
change, and assumes a yellow or ferruginous colour, 
an appearance commonly exhibited by the flints of 
our ])loughed lands. When in contact with ochra- 
ceoiis clay, or sand containing iron, it frequently 
attiiins a dark carnelian colour externally, the in- 
terior being of a lighter shade : of this kind, nume- 
rous 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 zoo- 
})hytal organization. These nodules oftentimes 
exhibit not only the outline of the original zoo- 
phyte, 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 crystallised 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 extensive scale, the siliceous no- 
dules, whose history is the subject of these remarks, 
afford the most conclusive evidence. At the pre- 
* “ So far as my observation extends, zoophytes appear universally 
to have formed the nuclei of nodulated and coated flints.” — Townsend's 
Character of Moses, 
