342 Account of a remarkable Fossil. (May, 
Artic.E II. 
Account of a remarkable Fossil. By Thomas Thomson, M.D. F.R.S. 
Tue fossil which is represented in Plate LXVI., Fig. 1, was 
found about a year ago in the parish of Alfold, in the county of 
Surrey, some miles east of Guildford. The part of the country 
where it occurred is very flat. ‘The petrifaction was met with about 
eight feet under the surface, ina bed of clay. But over the clay in 
that particular part is a bed of gravel, which extends to a consider- 
able distance east and west; and varying in breadth from 10 or 12 
yards to about a furlong. This bed of gravel is bounded on every 
side by clay, and has very much the appearance of having been 
formerly the bed of ariver now driedup. The soil over the gravel 
is much more fertile than that over the clay. . 
The specimen represented in the figure is nearly square, and 
about four inches in length, and nearly as much in breadth, Three 
or four pieces of nearly the same size were found at the same time; 
but the workmen who discovered them unluckily destroyed them. 
My specimen was fortunately preserved by falling into the hands of 
Myr. John Street, of Birtley, to whom | feel myself under great 
obligations for having politely presented it to me, when I had the 
good fortune to visit him last autumn, 
The mass of the specimen is a very hard clay, the upper surface 
of which is covered with scales lying in regular order. ‘These scales 
are thin rectangles, about three-fourths of an inch in length, and 
five-eighths of an inch in breadth. They have a brownish-black 
colour; but, when viewed against the light, are a fine hair-brown. 
Their lustre is shining and silky. Some of them have a semime- 
tallic lustre, somewhat similar to what often appears upon the scales 
of fish. Most of them, when viewed by candlelight, reflect a 
lustre somewhat similar to mother-of-pear]. These scales are too 
hard to be scratched by the nail; but they yield readily to the knife, 
and have, as nearly as I can determine, the hardness of bone. In 
many places they are rent or broken in different directions, and the 
rents are filled with the same clayey matter of which the specimen 
consists. ‘This clay cement has the appearance of thin veins in the 
scales. These scales are slightly translucent on the edges. They 
are very easily frangible. Sectile. Sp. gravity 2°54. When heated 
they decrepitate, and when kept in a red heat they become white, 
as is the case with bone. 
I kept 2°9 gr. of these scales for half an hour red-hot in a pla- 
‘tinum crucible. The weight by this exposure was reduced to 2°57 gr. 
The portion of scale had become grey, but was not quite white. 
The 2°57 gr. dissolved with effervescence in nitric acid, and left a 
small charry residuum, which | could not weigh, but which could 
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