P. F, Kendali—Aragonite Shells in the Coralline Crag. 497 
claims for it; and this, in the face of the paleeontological facts which 
I have pointed out, is the reverse of likely. 
These were the facts in 1843 and 1845; since which time I have 
not visited the Barton-Hordwell Cliff, though I have (in 1856) the 
opposite one of the Isle of Wight; the drawings I then made of 
which, from Sconce Point to Alum Bay complete, lead me to regard 
the view of it taken by Messrs. Keeping and Tawney, in their paper 
of December, 1880, and by the Geological Survey, as correct. 
TV.—Own tue DissonutTion or ARAGONITE SHELLS IN THE CORALLINE 
CRAG. 
By Percy F. Krenpatu. 
An 1879 Mr. Sorby in his Presidential Address to the Geological 
Society published the result of his investigations into the 
question of the extent to which the mineralogical constitution of 
shells, ete., influenced their preservation as fossils. 
He pointed out that the two forms of carbonate of lime—calcite 
and aragonite—occur in the hard parts of various Invertebrates, 
and that aragonite, though harder and of higher specific gravity 
than calcite, is a less stable substance, and is much more easily 
acted upon by carbonated water. This would of course tend to 
the dissolution of aragonite structures under circumstances which 
might permit of the preservation of calcite, and he instanced the 
shells in a raised beach, in which he observed that those shells which 
were composed of an inner aragonite and an outer calcite layer had 
lost the inner layer altogether. 
Mr. Sorby’s classification is as follows :— 
CALCITE. ARAGONITE. 
Foraminifera. Corals. 
Annelids. Cephalopoda. 
Echinoderms. Gasteropoda, except Patella, Fusus, Lit- 
Polyzoa, containing also some aragonite. torina, Purpura, and some others. 
Brachiopoda. Conchifera, except Ostrea, Pecten, and 
Ostrea and Pecten. the outer layer of Spondylus, Pinna, 
Cirripedia and all other Crustacea. and Mytilus. 
During some recent work in the Crags of Essex and Suffolk 
I have observed a very remarkable confirmation of Mr. Sorby’s 
conclusions. 
The Upper beds of the Coralline Crag are in most places coherent 
enough to retain casts of organisms which may have been dissolved 
from them, and such casts have been noticed by geologists since the 
time of Dr. Mantell, whose collection in the Natural History Museum 
contains one from a pit at Aldeburgh. To this pit my remarks will 
chiefly apply. Here well-preserved shells and other remains are 
very abundant, indeed there is no place where such a profusion of 
beautiful and delicate Polyzoa can be obtained, but besides these 
there are many casts of shells to be seen in the matrix, the shells 
themselves having been completely dissolved away. Tabulating 
these as below, I find that with one exception the whole of the shells 
DECADE II.—VOL. X.—NO. XI. 382 
