5T0 Dr Brewster's Reply to Mr Brookes Observations 
must ever remain blind. . These composite minerals, often re- 
sembling homogeneous minerals in their external form, are now 
so numerous, that it has become necessary to establish a new 
system of crystallisation for the purpose of receiving them, not 
merely because they are entirely different bodies from homo- 
geneous crystals, but because they are formed by new laws and 
new principles of combination, which philosophers have vet to 
develope. Crystallography will then be divided into Five Sys- 
tems : 
1. The Rhomboidal System, 
% ; The Pyramidal Sytem. 
8. The Prismatic System. 
4. The Tessular System ; and, 
5. The Composite System. 
Having thus removed every objection that has been urged, 
either against the accuracy or generality of the optical method^ 
I shall now briefly contrast it with the crystallographic method, 
in reference to their power of discovering new minerals. It would 
require the limits of a volume to explain the various characters, 
of mineral bodies which the optical method supplies. They are 
of the most palpable and definite kind and connected as they 
are with some of the most curious researches of modern science, 
they elevate Mineralogy from a descriptive branch of Natural 
History to a lofty station among the Physical Sciences. I 
might here adduce numerous instances where these characters* 
have led to the immediate discovery of new minerals, when crys- 
tallography supplied no discriminating tests ; but I shall confine 
myself to two cases, which have a special application in the pre- 
sent discussion. The minerals of the Zeolite family having been 
particularly examined by Mr Brooke and by myself, we have 
had occasion to apply our respective methods of observation to 
several minerals which had not been carefully studied by pre- 
ceding mineralogists. Two of these minerals were the NadeU 
stein of Faro , and a mineral from Aix-la-Chapelle, supposed by 
Haiiy to be a Stillite *. All the resources of crystallography 
* A description of this mineral, to which I have given the name of IJopeife, 
was read before the Royal Society of Edinburgh on the 17th June, and will appear 
m the next volume of their Transactions. The Nadehtein from Faro is a raos'5 
