BENSTED— ON THE GEOLOGY OF MAIDSTONE. 



370 



traced in the hassock without difGculfcy from its clear blue colour, 

 and by being composed of limestone. Within the stem a pith or cavity 

 runs foi" a considerable distance, aiul portions liave a ferruginous tinge. 

 Very large specimens show the branched form of this organism. 

 Another " soft limestone " next occurs, the same character as tliat 

 recorded above. 



The "soft hassock" (No. 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 stria? wliich 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 

 is of a flat oblong shape, about eight inches one way by five the 

 other, and three inches thick. It has some Tlustra 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 shell 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 interesting ; 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 spiculsD of dead sponges. The skeleton of a marine tur- 

 tle was found not very far off, 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 Wales or 

 some parts of Africa contains abundance of spicul^e 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 witli the sand and de- 

 taehed spicuhc, but the boulder was ])robably 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 difh- 

 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 Oreensaiul sea, which was inhabited by tropical species 

 of shells and zoophytes. 



