IIORTON — GEOLOGY OF THE STONESFIELD SLATE. 
257 
reptiles the Pterodactyles arc represented by one species (P. BucJc- 
landi), cliiefly known by its wing-bones, remarkable foi- ilieir Icngtli, 
and which, like those of birds, were hollow in the middle, thus com- 
bining extreme lightness with strength. The family of turtles are 
known in these beds by one small species of Chelonia. 
The remarkable catalogue of associated life exhibited by these rocks 
is rendered still more complete by the occurrence of three genera of 
Mammalia, namely, Amjjhithcrium, Phascolothcnum, and StereognatJiMS. 
Of these the only known remains are a few specimens of the lower jaws, 
with small cuspidated teeth, indicative of a small insectivorous quad- 
ruped, probably allied to the opossums, and other marsupial genera 
now confined to Australia and Tasmania. It is extremely intei'csting 
to observe that this resemblance to existing forms of Australian life is 
by no means limited to the mammalia of the Oolite. For instance, 
in the Australian sea exists the Cestrmion PJiilUjji, or Port Jackson 
shark, the only kno\\Ti representative of the numerous species of 
Acrodi and Strophodi, the palatal teeth of which are so abundant in 
the Oolitic beds. There also living Terebratulse are found associated 
with a species of Trigonia, the extinct forms of which are among the 
most common of the Stonesfield fossils. On the continent of 
Austi'alia also flourish the Ai^aucarite and Cycadacese, coniferous 
plants, very nearly allied to the vegetable remains of the Stonesfield 
Slate. 
If we review the fossil treasures of Stonesfield in the aggregate, we 
can to some extent reproduce that period of the earth's history in 
which the district under our notice was a lagoon with boidering 
mai'shes, intervening between a line of coast on the one hand, and 
the ancient Oolitic ocean on the other. Every cn-cumstance con- 
nected with these finely laminated and ripple-marked sandstones 
indicates the nature of the process by which they were deposited 
to have been slow and gradual, doubtless demanding similar con- 
ditions to those which would prevail in a shallow sea-lake, pene- 
trated at intervals by moderate swells, or gentle tides from the 
sea, but not exposed to storms or fluctuations caused by violent 
littoral action. 
We may picture to ourselves the inliabitants of this lagoon, consti- 
tuting a large population, beautiful branching star-corals analogous to 
those forming the reefs and islets on which the broad Pacific smiles, 
aristocratic Nautili and Ammonites associated with their humbler 
neighbours, the Trigoniis, Terebratulge and oysters that fm'nished a 
supply of food for the nmnerous sharks and other predaceous fishes 
infesting the wide open sea, and frequently visiting this quiet lake in 
quest of prey. On the ancient land lived that monstrous reptile the 
Megalosam-us and the crocodile-like Teleosam-us, -with a few turtles ; 
strange winged lizards, the Pterodactyles, hovered in the air, or 
snatched their prey from the calm waters below ; and insects like 
dragon-flies flitted over the reedy marshes. Prom time to time 
fragments of bordering plants floated in the shallow pools, 
either swept down by inundations or driven by the wind ; 
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