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VIII. Some Obfervations on the Hardnefs 
of Shells, and on the Food of the Soal- 
Fifh \ by Mr. Peter Collinfon, F. R. S. 
Read March 15. TT HAVE obferved feme Circumftances 
1744- j n t | ie Structure of Shells, which I 
know not whether they have been fufficiently at- 
tended to 3 I mean their durable Hardnefs andPolifh; 
which, in the flendereft of thefe Bodies, is very re- 
markable; and it is unknown how long they will 
refill the Injuries of Time and Weather. 
1 faw an Inflance of thefe permanent Qualities at 
St. Edmond’ s-bury-> in the Ruins of that Abbey, which 
is built of a kind of Stone compofed of Grit or Sand, 
interfperfed with an infinite Number of very minute 
Shells, which appeared to be a Species of fmooth 
fhining Cockle. In feveral Parts of the Building, 
much expofed to the Air, the Sand was mouldered 
away ; but thefe exceeding fmall Shells remained 
intire, and their Polifh not in the lead decayed. 
It may be alledged, that a petrifying Juice, the 
fame that had united the Paiticles of the Sand 
together, had likewife hardened thefe, and ren- 
dered them more durable than Nature had formed 
them. 
But, as we have many Inftances of Shells retaining 
their natural Politure and Firmnefs, where no fuch 
Allegation can juftly be made (for Inftance, the 
Shells found in Chalk pits, in Loams, and feveral 
other Places, where no fuch juices are hitherto proved 
to 
