3io 
Mr. Tennant on different Sorts 
it, and no quarries of a similar kind are known in Italy ; the 
second was said to have been thrown up by Mount Vesuvius ; 
and the third was from Iona, one of the western islands of 
Scotland. In many kinds of common marble, small particles 
and veins may be observed, which are a long time in dissolving. 
These, upon examination, I discovered to contain a considerable 
proportion of magnesia ; but, as they were probably not quite 
free from the surrounding marble, I did not ascertain the quan- 
tity precisely. 
The crystallized structure which may generally be observed 
in the magnesian limestone, seems to shew that it has not been 
formed by the accidental union of the two earths, but must 
have resulted from their chemical combination. The difficulty 
of dissolving it, may also arise from the attraction of the different 
component parts to each other. The mortar formed from this 
kind of lime, is as soluble in acids as common marble ; and the 
substances of which it consists are easily separated. The mag- 
nesia may be taken from it by boiling it in muriated lime, and 
lime is precipitated by it from lime water; but neither of these 
effects can be produced by the stone, before it is calcined. 
Magnesian limestone is probably very abundant in various 
parts of England. It appears to extend for thirty or forty miles, 
from a little south-west of Worksop, in Nottinghamshire, to 
near Ferry-bridge, in Yorkshire. About five or six miles further 
north there is a quarry of it, near Sherburfl; but, whether 
this is a continuation from the stratum near Ferry-bridge, I 
have not learnt. From some specimens which were sent me, 
I find that the cathedral and walls of York are made of it. I 
have not been able to learn whether there were any shells in 
the limestone of the tract of country before mentioned. In Mr. 
