TAB. XV. 



SI LEX arenacea, var. calcarea. 

 Calcareous Sandstone. 



Class 2. Earth. Ord. 2, Mixed. 



Gen. 6. Silex. Spec. 2. Combined with calcareous Earth, 



Div. 2. Semi-indurated, 

 Syn. Calcareous sandstone. Kir, v. 1. 361. 



jVIasses of this, from about 8 inches to 2 feet thick, were 

 found at near twelve feet deep in a light gravelly stratum, in 

 cutting the canal at the Isle of Dogs, The decomposing 

 shells have apparently undergone a change, by means of 

 subterraneous heat causing them to combine with the sand 

 and pebbles. Some of the shells I believe are new to Great 

 Britain, both in the natural and fossile state. These are the 

 -gibbous Area, at the lower corner on the right hand, the 

 hinge and cockle-like edge of which are seen distinctly 

 above it ; the oblong Area resembling a Mytilus, on the left 

 side, showing part of the hinge, which I have not seen in any 

 other specimen. The decomposition of this shell, and the 

 Turbo near it, are more chalky than the others. The oblong 



