22 
Proceeding* south-westward, from the well defined part in North Wilts, its course, in or near 
the same high ground as the Stratum before described, narrows much, but like that stone spreads 
again in the broad vale of Blackmoor, following the outcrop of the Coral Rag and Pisolite Rock, 
past the River Stour ; further westward, where the stony land is deficient, the course of the 
Chinch Clay is less distinct, and here, as in the north, is not likely to be identified, or clearly 
distinguished from the other Clays above it, but by the organized Fossils in wells and other 
excavations. 
But for these, and the numerous experiments for coal, the nature and contents of these 
clayey Strata deep in the earth could not have been known 
By some of the perforations in Wiltshire, &c. it appears that the lower part of this thick 
Stratum is considerably laminated, and rises in large flat pieces, which when dried are slightly 
inflammable. 
Thus as the best and most delicate fossils of this Stratum will not bear exposure, they can be 
found only by persons employed in excavations, or those who overlook such works ; hence it 
would be fruitless to search for any but in those places ; and there being little inducement to 
make deep excavations in these strata, and no canals or other public works in hand, specimens 
of these fossils cannot be multiplied for collections, or will be obtained with difficulty. 
The lower part of this thick clay, like that of the one preceding, contains septaria stored 
with organized fossils, greatly resembling those of the stony Stratum beneath. 
Ammonites Calloviensis in mass are inclosed in these septaria, remarkably sharp and fine, 
with a whitish exterior, but are liable to decomposition from the oxydation of the Sulphuret of 
Iron they contain. 
The beautiful specimens many years since dug up from my good friend Mr. T. Crook’s 
estate, in a large septarium lying in clay, are omitted in this Stratum, the same species being 
figured as characteristic of the rock beneath. 
In this as in several other instances where the bottom of the clay contains the same fossils as 
the rock which it covers, it is difficult to determine to which Stratum they belong. 
ORGANIZED FOSSILS . 
Dudgrove Farm. 
Derry Hill. Meggot’s Mill, ColeshilL Tytherton 
Lucas. Dudgrove Farm. 
FIG. 
1 Belemnites - . - 
2) Gryphasa dilatata 
33 
4 Ammonites 
5) Serpula - 
63 
The upper part of this thick Stratum contains large incurved oysters or Gryphma, so much 
resembling others I have collected from remote parts, of a clay which now appears to be Oak- 
tree cl ay,as to be distinguished with difficulty ; but this is only one of the many instances of 
the general resemblances of organized Fossils, where the Strata are similar. 
Tytherton Lucas. Thames and Severn Canal. 
Wilts and Berks Canal, near Chippenham. 
