Discovery of the Composition of the Arragonite. 
has scffered to a most wonderful extent by decomposition ; 
bni «here it retains its freshness, no granite can possibly 
be better characterized. The specimens which [I was able 
to bene away, and which are now before the Society, are 
by mo means adequate to convey an idea of the coarse tex- 
ture it sometimes presents. In the granite of Dartmoor, 
the crvstals of felspar are uncommonly large, often four 
inches tn length. 1 believe it was from this neighhourhood 
that the favs of the footpath on Westminster Bridge were 
broueht; in these, crystals of felspar nearly as large may be 
observed. 
[To be continued.] 
= 
Ill. Discovery of the Composition of the Arragonite. Ina 
Letter from Professor StrROMEYER of Gottingen to Pro- 
fessor Gitwert of Leipzig. Dated 23d Feb, 1813. 
Tu: arragonite is one of the minerals on the analysis of 
which I have been employed this winter. You will be sur- 
prised that I have attempted to submit this substance to a 
new analysis, when it had been already investigated by 
Klaproth, Vauquelin, Fourcroy, Bucholz, Thenard, and 
Biot, who had unanimously declared it to be carbonate of 
lime, differing neither in the quality, nor in the quantity of 
jts component parts from the common rhomboidal crystals. 
However accurate and demonstrative their experiments ap- 
peared to be, I confess I have always entertained some 
doubt of their sufficiency ; since such a case of a structure 
totally different, without any difference in the composition, 
would be completely singular, and at variance with every 
ether fact in crystallography and crystallotomy. [ am 
therefore particularly happy in being able to announce to 
you, tbat I have at last succeeded in discovering an essential 
difference between the arragonite and the crystal'ized car- 
bonate of lime, and to remove this striking contradiction 
from the science. The arragonite contains, besides car- 
bonate of lime, also carbonate of strontia, chemically united 
with it in a constant proportion, and constituting a true 
natural triple combination of the carbonic acid with lime 
and strontia. The quantity of the carbonate of strontia in 
the arragonite amounts to between 3 and 4 per cent. That 
so great a quantity of carbonate of strontia should escape 
the notice of those who have examined this mineral, I can 
only atiribute to this circumstance ; that they have consi- 
dered the sulphate of strontia as equally insoluble in water 
with 
