Cn. XX.] STONESFIELD SLATE. 309 



the genera Patella, Nerita, Rimula, and Cylindrites are common (see 

 figs. 369 to 372) ; while cephalopods are rare, and, instead of ammonites 

 and belemnites, numerous genera of carnivorous trachelipods appear. 

 Out of one hundred and forty-two species of univalves obtained from the 

 Minchinhampton beds, Mr. Lycett found no less than forty-one to be car- 

 nivorous. They belong principally to the genera Buccinum, Pleurotoma, 

 Rostellaria, Murex, Purpuroidea (fig. 368), and Fusus, and exhibit a 

 proportion of zoophagous species not very different from that which ob- 

 tains in warm seas of the recent period. These chronological results are 

 curious and unexpected, since it was imagined that "^^e might look in 

 vain for the carnivorous trachelipods in rocks of such h.gh antiquity as 

 the Great Oolite, and it was a received doctrine that they did not begin 

 to appear in considerable numbers till the Eocene period, when those two 

 great families of cephalopoda, the ammonites and belemnites, had become 

 extinct. 



Stonesfield slate. — The slate of Stonesfield has been shown by Mr. 

 Lonsdale to lie at the base of the Great Oolite.^ It is a slightly 

 oolitic shelly limestone, forming large spheroidal masses imbedded in 

 sand, only 6 feet thick, but very rich in organic remains. It contains 

 some pebbles of a rock very similar to itself, and v/hich may be portions 

 of the deposit, broken up on a shore at low water or during storms, and 

 redeposited. The remains of belemnites, trigonise, and other marine 

 shells, with fragments of wood, are common, and impressions of ferns, 

 cycadecC, and other plants. Several insects, also, and, among the rest, 

 the wing-covers of beetles are perfectly preserved (see fig. 

 373), some of them approaching nearly to the genus Bupres- 

 tis.\ The remains, also, of many genera of reptiles, such as 

 Pleiosaur, Crocodile, and Pterodactyl, have been discovered in 

 the same limestone. 



But the remarkable fossils for which the Stonesfield slate 

 is most celebrated, are those referred to the mammiferous 

 class. The student should be reminded that in all the rocks 

 described in the preceding chapters as older than the Eocene, 

 Buprestisf no bones of any land quadruped, or of any cetacean, have 

 stonesfiftid. bgen discov ?red until the Sixdacotherium of the Purbeck beds 

 came to light in 1854 (see above, p. 295). Yet we have seen that ter- 

 restrial plants were not rare in the lower cretaceous formation, and that 

 in the Wealden there was evidence of freshwater sediment on a large 

 scale, containing various plants, and even ancient vegetable soils. We 

 had also in the same Wealden many land reptiles and winged insects, 

 which render the absence of terrestrial quadrupeds the more striking. 

 The want, how-ever, of any bones of whales, seals, dolphins, and other 

 aquatic mammalia, whether in the chalk or in the upper or middle 

 oolite, is certainly still more remarkable. Formerly, indeed, a bone 



* Proceedings Geol. Soc. vol. i. p. 414. 



f See Buckland's Bridgewater Treatise ; and Brodie's Fossil Insects, where it 

 is suggested that these elytra naay belong to Prionus, 



