346 
ELEMENTS OF GEOLOGY. 
Fii?. 838. 
but very rich in organic remains. It contains some pebbles 
of a rock very similar to itself, and which may be portions 
of the deposit, broken up on a shore at low water 
or during storms, and redeposited. The remains 
of belemnites,trigonia3, and other marine shells, with 
fragments of wood, are common, and impressions of 
ferns, cycadese, .and other plants. Several insects, 
also, and, among the rest, the elytra or wing-covers 
of beetles, are perfectly preserved (see Fig. 338), 
some of them approaching nearly to the genus Bu~ 
prestis. The remains, also, of many genera of rep¬ 
tiles, such as Pleiosaur^ Crocodile^ and Pterodactyl^ 
Elytron of have been discovered in the same limestone. 
i^onSfieid remarkable fossils for which the Stones- 
* field 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, no bones of any land-quadruped, or of 
any cetacean, had been discovered until the Spalacotherium 
of the Purbeck beds came to light in 1854. Yet we have 
seen that terrestrial plants were not wanting in the Upper 
Cretaceous formation (see p. 302), and that in the Wealden 
there was evidence of fresh-water sediment on a large scale, 
containing various plants, and even ancient vegetaMe soils. 
We had also in the same Wealden many land-reptiles and 
winged insects, which render the absence of terrestrial quad¬ 
rupeds the more striking. The want, however, of any bones 
of whales, seals, dolphins, and other aquatic mammalia, wheth¬ 
er in the chalk or in the upper or middle, oolite, is certainly 
still more remarkable. 
These observations are made to prepare the reader to ap- 
•preciate more justly the interest felt by every geologist in 
the discovery in the Stonesfield slate of no less than ten 
specimens of lower jaws of mammiferous quadrupeds, be¬ 
longing to four different species and to three distinct gene¬ 
ra, for which the names of Amphitherium^ Phascolotherium^ 
and Stereognathus have been adopted. 
It is now generally ad- Fig. 339. 
mitted that these are really 
the remains of mammalia 
(although it was at first 
suggested that they might 
be reptiles), and the only Tupaia Tana. 
question open to contro- Natural size 
versy is limited to this 
point, whether the fossil mammalia found in the Lower Oolite 
Right ramus of lower jaw. 
A recent insectivorous pla¬ 
cental mammal, from Sumatra. 
