132 Rejoinder of Prof. Shepard to Prof. Del Rio. 
ples I have advanced, which are very unaccountably supposed to 
preclude all regard to a difference of color and lustre between these 
species. My treatise however is very explicit in the definition of the 
natural properties of minerals, and in the enumeration of these prop- 
erties among them. His assertion that I exclude color, fracture and 
lustre, from the list of natural properties, is farther proof of the hasty 
manner in which he has considered the subject of his criticisms; and 
has no better foundation than my having pronounced identical the 
three varieties of Galena proposed by him as a puzzle for the pu- 
pil using my book. These varieties were supposed to differ in 
structure: one of them is crystallized in the form of the cube, an- 
other massive in large individuals, and the third fine granular. How 
it is possible for these varieties to be identical in the sense of Natu- 
ral History, will appear, if any one will peruse the remarks on Iden- 
tity, § 104, p. 30 of my Treatise, and that without overlooking struc’ 
ture, color and lustre, as natural properties. 
Prof. Dex Rio is at a loss to understand how the frequent divis- 
ion of the species is a consequence, as | had asserted, of providing 
means for the determination of imperfect minerals. When any one 
will attempt to secure the object at which I aimed, in a manner 
equally effectual, he will probably comprehend the nature of the ne- 
cessity. I intended by the remark, however, simply to say that I 
could not accomplish the task and avoid such a division. Should it 
be performed without involving this inconvenience, my assertion will 
be found untrue, and I shall cheerfully encounter the mortification it 
may occasion, for the sake of the improvement; though I must de- 
ny having triplicated (as charged by my reviewer) or even dupiicalets 
the species by the process I have adopted. 
- Prof. Dex Rio recommended the arrangement of Leucite, Anal- 
cime and Garnet under a new order, the trapezohedron. I had a 
right to conclude that this was done as likely, in his opinion, to lead 
the pupil to the names of these minerals with greater facility than 
on the disposition I had made of them. In adhering to my arrange- 
ment, therefore, I do not perceive the impropriety of saying, in re- 
ply, that it would lead to no confusion, provided I showed satisfac- 
torily, as I trust I did, that none could occur 
I notice also with regret, that Prof. DetsBad adheres to his for- 
mer assertion concerning the determination of Quartz, as included in 
my order of the rhomboid; and that he has become so extravagant 
as to deny that it ever presents itself under the figure of its primi- 
