BENSTED — ON THE GEOLOGY OF MAIDSTONE. 
379 
traced in the hassock without diflficulty from its clear bhie colour, 
and by being composed of limestone. Within the stem a pith or cavity 
runs for a considerable distance, and portions have a ferruginous tinge. 
Very large specimens show the branched form of tins organism. 
Another " soft limestone " next occurs, the same character as that 
recorded above. 
The "soft hassock" (Xo. 15) has some interest attached to it by 
the discovery of a tooth of the Polyptychodon, of a much larger size 
than the one described at page 338. The enamel of this tooth is so 
friable that much of it shivered off in clearing away the sandstone 
which enveloped it, but enough remains to show the ^riae which are 
one of its characteristic features. A rolled pebble or boulder of granite 
was found in this bed of " spiculae hassock ;" it weighs 8|- lbs., and 
13 of a flat oblong shape, about eight inches one way by five the 
other, and three inches thick. It has some Flustra attached to its 
surface, and the impression of a Trigonia is perceptible on one side. 
The latter seems to have been caused by the weight of the superin- 
cumbent strata pressing the shel) close on the surface of the granite, 
although how the tracery of its form was impressed on so hard a sub- 
stance is not easily to be understood. The Trigonia has not entered 
the boulder, but the outline is on the surface. For the granite, how- 
ever, it is a seal identifying its locality. The occurrence of a fragment of 
primitive rock in a Secondary formation is iuteresting ; and its solitary 
occurrence in a bed free from pebbles, and even coarse sand, gives 
rise to speculative conjecture as to the means of its envelopment. 
The sand is of very fine texture, and contains an immense quantity 
of detached spiculae of dead sponges. The skeleton of a marine tur- 
tle was found not very far oft', and a tooth of Polyptychodon occurred 
near the same spot. We have now causes in action giving rise to 
similar results. The sand from the coasts of New South AVales or 
some parts of Africa contains abundance of spiculae of all descrip- 
tions ; the same is the case with the sand from the West India Is- 
lands, arising from the decomposition of myriads of spongeous bo- 
dies with which the bottom of the seas in those regions is covered. 
There can be no doubt but that the sand of the sandstone of the 
Lower Greensand here has been accumulated under similar circum- 
stances. Skeletons of the turtles, and teeth and bones of the fishes 
inhabiting that ancient sea, are found mingled with the sand and de- 
tached spiculae, but the boulder was probably rolled into its spherical 
figure in association and in contact with fragments of rock of equal 
size and hardness with itself. The presence of the cells of the deli- 
cate Flustra shows clearly that it had not been rolled in the sand in 
which it was enveloped, and the attachment of a small shell to its 
surface indicates a tranquil state of the waters around it. It is difii- 
cult to account for its presence. Icebergs are known to transport 
fragments of rock to a considerable distance, but an objection to the 
iceberg-carriage is found in the present case in the high temperature 
of the Lower Grreensand sea, which was inhabited by tropical species 
of shells and zoophytes. 
