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SECOND REPORT- IS 32, 
to differ in their inclination no less than 3°. Similar irregularity 
was found to exist in the crystallization of idocrase, and of 
tetragonal copper pyrites ; and at last, as he says, it seemed 
to be time to satisfy himself that there really was such a thing 
as a regular square pyramid in nature. This he fortunately 
discovered in a perfect crystal of zircon. In attempting to 
systematize these anomalies he has been led to introduce a 
number of new terms and laws, which perhaps may be less 
necessary when we have a fuller view of the facts of these and 
similar cases. 
All this unexpected uncertainty shows us how assiduously 
we ought to measure and compare crystals, if we wish to bring 
mineralogy into the form of a science either certain or syste¬ 
matical. The invention of the reflecting goniometer by Dr. 
Wollaston, was an invaluable gift to the crystallometer; and 
every step of our progress makes us more sensible of the im¬ 
portance of this elegant and well-devised instrument. But un¬ 
less we can acquire some knowledge of the laws of constancy 
and of change in the angles which we measure, this instrument 
is valuable only as an ingenious means for an undiscovered pur¬ 
pose, a precise expression in an unknown tongue. 
Perhaps we cannot deny that at present we have still to learn 
the true place of the isomorphous or plesiomorphous groups, 
and that we are ignorant on what step of the ladder of classi¬ 
fication they ought to stand;—whether they correspond to 
species, or to some higher division ;—and whether they contain, 
within the groups themselves, a further definite subdivision into 
subordinate members. 
The confusion and perplexity in which this branch of the 
subject is still involved, may be judged of in some measure 
from the fact, that in the course of last year Gustavus Rose 
published a very interesting memoir “ Onthenecessity ofuniting 
Augite and Hornblende into one species" ; thus throwing a 
doubt on the distinction of two minerals which had hitherto 
been supposed to be as clearly separated by their form and 
physical properties as any two species composed of similar 
ingredients. His grounds for maintaining their identity are 
not slight;—they are, the possibility of reducing the one form 
to the other, the resemblance of their chemical composition, 
but especially the mode of their occurrence in combination, and 
the fact that melted hornblende crystallizes as augite. 
Another indication of the same kind may be found in Mr. 
Kobell’s memoir on Diallage and Hypersthene. He conceives 
that these minerals may be traced to an agreement with pyro¬ 
xene, both as to their crystaliometrical and their chemical pro- 
