Co 
Ca 
TAB. CCXVII. 
-CALX carbonata, magnesiata. 
M. agnesian. Limestone. 
Class 2. Earths. Order 1. Homogeneous. 
Gen, 3. Calx. Spec. 5. Carbonata. 
Var. Magnesiata. 
Dw. 1. Crystallized. 
Syn. Magnesian Limestone. Zennant in Phil. Trans. 
1799, part 2. 
Mr. Tennant having favoured me with specimens of the 
stones spoken of in the Philosophical Transactions for 1799, 
I feel a pleasure in presenting so useful a subject to the 
public under such authentic circumstances. 
The upper figure is what may be called the petrified re- 
mains of a shell, and is of a remarkable construction, espe- 
cially on the hinge end. It has something of the ap- 
pearance of an Arca, but is very different, however, from 
any that I have before seen, either petrified or recent. It 
was a curious circumstance that caused Mr. Tennant’s in- 
vestigation of the nature of these Limestones ; for he ob- 
served in Mr. Marshall’s Account of the Agriculture of the 
Midland Counties, that the Limestone found at Breden, 
near Derby, is destructive to vegetation. His experiments 
confirmed this account; and he found it to depend on the 
Magnesia, of which it seems that this Limestone contains 
about a fourth part. He further remarks, on the authority 
of Dr. Fenwick of Newcastle, that the farmers in that 
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