32 
THE GEOLOGIST. 
rock is made up of 5/-_yo^o«— perfect and in fragments — with some Pedens, 
Terehratuhp, Echinoderms, &c. 
Sometimes this rock appears like friable chalk, without distinct fossils. A 
large natural pit, originating from the infalling of a cave, occurs near the ex- 
tinct volcano, Mount Gambler, and is ninety feet deep, showing a considerable 
thickness of this Bryozoan deposit in several beds of fourteen feet, ten feet, 
and twelve feet in thickness. Similar pits show the deposit in the same way 
at the Mosquito Plains, seventy miles north. 
Regular layers of flints, usually black, rarely white, occur in these beds, from 
fourteen to twenty feet apart. These, with its colour, and with the s\iperficial 
sand-pipes, perforating the rock to a great depth, give it a great resemblance to 
chalk. 
The whole district is honeycombed with caves — always, however, in the 
higher grounds in the undulations of the plains. 
One of the eaves, m a ridge on the northern side of the Mosquito Plains, is 
two hundred feet long, is divided into three great halls, and has extensive side- 
chambers. The eaves have a north and south du-ection, like that of the ridge. 
The large cave has a great stalactite in it ; and many bones of Marsupialia are 
heaped up against this on the side facmg the entrance ; possibly they may 
have been washed up against this barrier by an inflowing stream. The dried 
corpse of a native Les in tliis cave. It has been partially entangled in tlie 
stalactite ; but this man was known to have crept into the cave when he had 
been wounded, some fourteen years ago. Many of the caves have great pits 
for their external apertvires, and contain much water. 
Some shallow caves contain bones of existing Marsupialia, which have 
evidently been the relics of animals that fell into the grass-hidden aperture at 
top. 
The caves appear in many caves to be connected with a subterranean system 
of drainage ; currents and periodical oscillations being occasionally observed in 
the waters contained in them. There is but little superficial drainage. One 
overflovring swamp was found by the author to send its water into an under- 
ground chamiel in a ridge of limestone. 
Patches of shelly sand occur here and there over the ten thousand nine hun-- 
dred and eighty square miles of country occupied by the wliite hmestoues ; but 
near the coast this shelly sand thickens to two hundred feet. 
A coarse limestone forms a ridge along the coast-line, and it contains exist- 
ing species of shells. This indicates an elevation of the coast of late date, and 
wliich probably is stiU taking place. 
Dec. 14. — 1. "On some llemains of Polyptychodon from Dorking." By 
Prof. Owen, F.R.S., P.G.S. 
Referring to the genus of Saurians which he had founded in 1841 on certain 
large detached teeth from the Cretaceous beds of Kent and Sussex, and which 
genus, in reference to the many-ridged or folded character of the enamel of 
those teeth, he had proposed to call Polyptycliodon, Prof. Owen noticed the 
successive discoveries of portions of jaws, one showing the thecodont implanta- 
tion of those teeth, which, with the shape and proportions of the teeth, led 
him to suspect the crocodilian afimities of PolyptocJwdon ; and the subsequent 
discovery of bones in a Lower Greensand quarry at Hythe, which, on the hypo- 
thesis of their having belonged to PolyptycJwdon, had led him to suspect that 
the genus conformed to the Plesiosauroid type. 
The fossils now exhibited by Mr. G. Cubitt of Denbies, consisted of part of 
the cranium (showing a large foramen parietale), fragments of the upper and 
lower jaws, and teeth of the Polyptycliodon interrupttts, from the Lower ChaUc 
of Dorking, and afforded further evidence of the plesiosauroid afiinities of the 
genus. Professor Owen remarked that in a coUectiou of fossils from the Upper 
