22 NATURAL HISTORY 
a darkish sort of marl, and are usually very small 
and soft; but in Clay’s Pond, a little farther on, at 
the end of the pit, where the soil is dug out for 
manure, | have occasionally observed them of large 
dimensions, perhaps fourteen or sixteen inches in 
diameter. But as these did not consist of firm 
stone, but were formed of a kind of terra lapidosa, 
or hardened clay, as soon as they were exposed to 
the rains and frost they mouldered away. These 
seemed as if they were a very recent production. 
In the chalk-pit at the northwest end of the Hanger, 
large nautili are sometimes observed. 
In the very thickest strata of our freestone, and 
at considerable depths, well-diggers often find large 
scallops or pectines, having both shells deeply stri- 
ated, and ridged and furrowed alternately. They 
are highly impregnated with, if not wholly com- 
posed of, the stone of the quarry. 
LETTER! IV. 
As, in my last letter, the freestone of this place 
has been only mentioned incidentally, I shall here 
become more particular. 
This stone is in great request for hearth-stones 
and the beds of ovens, and in lining of lime-kilns 
it turns to good account ; for the workmen use san- 
dy loam instead of mortar, the sand of which flux- 
es* and runs by the intense heat, and so cases 
over the whole face of the kiln with a strong vitri- 
* There may probably be also in the chalk itself that is burn 
ed for lime a proportion of sand, for few chalks are so pure as to 
have none. 
