298 
THE GEOLOGIST. 
the hole would expand upon the surface, and thus a rounded cavity 
Avould be formed, at the bottom of which the spring is now seen to 
issue (at A). 
The water of these chalk springs is highly charged with calcareous 
matter, obtained in flowing through the chalk fissures, and this is 
precipitated on the fragments of sticks, roots, and leaves, which fall 
into the streams. At Boxley Abbey very fine specimens of calcareous 
tufa may be procured, as may be also incrustations of fir-cones, etc., 
by placing them in the water near the spring-head. 
A spring of water at Cosington, bursting from the Lower Chalk, 
deposits a coating upon the stones in its course of a bright crimson, 
which at one time was considered to proceed from an impregnation 
of iron-pyrites, but has now been determined to be of vegetable origin. 
The fossils of the Gault most common are Ammonites, Hamites, and 
Inocerami. At the Yarnes great quantities of round nodular masses 
are found. On breaking these stones a nucleus with concentric 
waving lines is seen ; they take a polish without difiiculty. These 
nodules, so rich in phosphate of lime, have been conjectured to 
be coprolitic, but my opinion has long been that they are originally 
of zoophytic or spongeous origin, and that the presence of the phos- 
phate is attributable to deposition from the water of the Cretaceous 
sea, as portions of ammonites and inocerami are found to contain 
equally considerable quantities of phosphate. 
We now come to the Lower Greensand. — The AVhite or Bearsted 
sand lies immediately under the Gault, upon the red ferruginous 
sands. Tt is limited in extent, occurring only at certain places and 
in difierent states of purity. White Heath, near Hollingbourne, af- 
fording a very superior kind. I never heard of any fossils being 
found in it. 
The next deposit is the ferruginous sand, with layers of ironstone. 
These beds rise rather abruptly 
from beneath the Gault at Box- 
ILiruL^ ley and Sandling, at an angle 
or dip of 20 degrees. Sections 
b of these beds may be seen at 
the sides of most roads which 
lead to the Gault, where the 
Fig. 4. — a a, horizontal layer of ferruginous sand has been cut through in 
sandstone ; b b, etc., layers in a false strati- many places. The most com- 
mon fossils in these beds are 
casts of zoophytes or sponges, generally of a cylindrical shape. Some 
appear allied to Siphonia, having a bulbous head, the sand being loose 
or non-segregated in the interior. A few marine shells may be de- 
tected by close inspection, chiefly Terebratulfe. Trigonia alctformis 
occurs in a bank of this sand near Thornhills. In Sandling Wood 
about twenty feet of the sand is exposed, in which the ramification 
of a marine plant is seen to great advantage. In places rings of 
ironstone, circular and oblong, give an appearance of wavy lines, but 
by a little examination it mav be seen that these lines are sections 
