32 



THE GEOLOGIST. 



rock is made up of Bryozoa — perfect and in fragments — witli some Pedens, 

 Terebratulo', JEchinoderms, &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 ia 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 superficial 

 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 caves, in 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 caves have a north and south direction, like that of the ridge. 

 The large cave has a ^reat stalactite in it ; and many bones of MarsupiaHa are 

 heaped up against this on the side facing the entrance ; possibly they may 

 have been washed up against this barrier by an inflowing stream. The dried 

 corpse of a native lies in this cave. It has been partially entangled in the 

 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 apertures, and contain much water. 



Some shallow caves contam bones of existing Marsupialia, which have 

 evidently been the relics of animals that fell into the grass-hidden apertui-e 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 di'ainage. One 

 overflowing swamp was found by the author to send its water into an under- 

 ground channel 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 white limestones ; 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 

 which probably is stiU taking place. 



Dec. 14. — 1. "On some llemains of Polyptychodon from Dorking." By 

 Prof. Owen, P.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 PoIyptycJwdon, Prof. Owen noticed the 

 successive discoveries of portions of jaws, one shoAving the thecodont implanta- 

 tion of those teeth, which, with the shape and proportions of the teeth, led 

 him to suspect the crocodilian affinities of Polyptochodon, ; and the subsequent 

 discovery of bones in a Lower Greensand quarry at Hytlie, which, on the h}^o- 

 thcsis of their having belonged to Poh/pti/chodo/i, had led him to suspect that 

 the genus conformed to the Plesiosauroid type. 



The fossils now exhibited by Mr. G. Cubitt of Dcnbies, consisted of part of 

 the cranium (showing a large foramen parietale), fragments of tlie upper and 

 lower jaws, and teeth of the Poli/pfj/ehodou interrupt us, from the Lower Chalk 

 of Dorking, and afforded further evidence of the plesiosauroid aflliiitics of the 

 genus. Professor Owen remarked that in a collection of fossils from the Upper 



