483 



at the latter locality by the operations of the workmen in digging 

 brick earth. Fossils, chiefly belonging to the genera Ostrea, Cyclas, 

 and Cerithium, occur most in one particular part of the deposit 

 called the clay and shell bed: it consists of a bluish black, tenacious 

 clay alternating with shells which are tender and chalky. 



4. The London clay is of very small extent in the district de- 

 scribed by the author, but possesses the same characters as at 

 Shooter's Hill. It merely caps the hill below Upnor, and extends to 

 Hoo, with a breadth of less than ^ of a mile, and a length of 2^ 

 miles. 



5. The diluvium is met with on the slopes and tops of the hills, 

 as well as in the valleys. In the latter its average thickness is 6 

 feet, but in some situations it considerably exceeds 20 feet. On 

 the former it varies from 1 foot to 20 feet in thickness, with an 

 average of 2 feet. In situations not exposed to the action of 

 running water, as on the summits of the hills, it consists in the 

 lower part of water-worn chalk, mingled with displaced but unrolled 

 flints, which are often so friable as to fall to pieces when moved. 

 Above these lies a mixture of stiff red clay and flints, with occa- 

 sional seams of sand. The fossil remains discovered in this deposit 

 are the bones and teeth of the Elephant, Deer, Rhinoceros, and of 

 an unknown animal. 



6. The alluvial matter deposited by the present stream con- 

 sists of gravel and rolled pebbles, covered by dark blue clay and 

 vegetable remains, having a depth of ten feet or upwards. Its ex- 

 tent on both sides of the river proves that the Medway formerly 

 occupied a much greater breadth than at present; and the large 

 marshes below Chatham attest its tendency to accumulate. In fact, 

 the river is said to have perceptibly shallowed within the last forty 

 years. 



A memoir was afterwards read " On a Fossil in the Bristol Mu- 

 seum, and discovered in the Lias at Lyme Regis," by Dr. Riley, 

 and communicated by Charles Stokes, Esq., F.G.S., &c. 



After stating the different opinions which had been given by those 

 naturalists who had seen the specimen, and alluding to their apparent 

 incorrectness, the author states that he is induced to consider the 

 fossil as the remains of a cartilaginous fish, having many points of 

 resemblance to the Rays, but differing from them in several im- 

 portant characters. He then proceeds to give a minute description 

 of the anatomical structure of the fossil, commencing with the head. 

 He states that the jaws are very much elongated; that he could dis- 

 cover in the upper no traces of respiratory canals or openings ; that 

 it appears to have fitted into a central groove in the lower jaw; that 

 there are no signs of any cavities for the reception of teeth; but that 

 there are lying near the jaws many spines with radiate bases similar to 

 the spines of rays and other cartilaginous fishes. The orbits are stated 

 to be of immense size, surrounded by an elevated edge or ridge, 

 and the space on each side of the median line and within these ridges 

 and corresponding to the parietal and frontal bones, to be flat and 

 depressed not unlike that of a Saurian ; but the author considers 



