148 S. P. Woodward—WNature and Origin of Banded Flints. 
of a third form of Sponge, through which the bands pass un- 
concerned; and the critical example (Pl. VIL, fig. 5) exhibits 
both in long and cross section a well-defined sponge, permeated 
by canals like the stem of a Siphonia, which appears to be 
equally unaffected by the passage of the coloured zones. 
Equally conclusive of the inorganic origin of the banded 
tracts in flints are the specimens in which they are connected 
with ancient fractures formed while yet én siti in the Chalk. 
Flints thus broken, and subsequently re-cemented together, have 
been frequently noticed. In the one represented by Pl. VIIL., 
fig. 2, there is a minute displacement, visible externally at 
either end (2). The flint is broken along the line of fissure, 
and shews the side of the vein of white flint filling it, while a 
second fracture at right angles shews the relation of the banded 
infiltration. Fig. 3 1s a similar flint, broken so as to shew on 
each side, the banded tract bordering the plate of cementing 
flint, and also along the plane of this old fracture. Waterworn 
pebbles formed from flints of this description have been found 
by Mr. Wetherell in the gravel-pits of Muswell Hill. 
I take this opportunity to give some account of another 
banded flint, which, though outwardly resembling some of those 
already mentioned, has had a very different origin. The 
specimen represented by Pl. VIIL., fig. 4, is part of a vein from 
a fissure in the Chalk at Dover, and was presented to the 
British Museum in March 1862, by Mr. John D. Richardson, 
one of the contractors for the extensive works then in progress 
for increasing the fortifications on the west face of Dover 
Citadel. The Chalk-pits in some parts of England, as in 
Hampshire, exhibit more than elsewhere the phenomenon of 
inclined and vertical fissures filled with flint, which consists of 
two or more lamin separated partially by a central layer of 
chalky or ferruginous earth. These veins establish the fact of 
the deposition of flint by water flowing through it, like mineral 
springs, after the consolidation and movement of the Chalk. The 
fissure at Dover appears to be filled up chiefly with Chalk, and 
only in one horizon by a grey siliceous deposit, which has re- 
united a broken course of flints. It contains minute angular 
fragments of the black flint that seem to have occasionally 
fallen in and become imbedded. The current flowing through 
the fissure gave to its contents a laminated arrangement, and 
formed a deep central groove which appears to have been con- 
tinuous in all the deposited layers, chalk and flint alike. 
Mr. Richardson states in his letter that the vein of banded 
flint was met with in cutting through the Chalk-ridge that 
runs parallel with the coast, and about opposite the Shakespear 
