320 Mr. Shejpard's reply to Prof. Del Rio. 



Nor can any confusion be experienced in the determination of 

 the Leucite, from the fact that it has a dodecahedral cleavage, while 

 I place it under the cube ; for it is not likely that the pupil will dis- 

 cover either the cubical or the dodecahedral cleavages, (both of 

 v/hich, however do exist) but will, if he follows the directions of 

 the Treatise,* try the order of the cube first, where he will find it. 



I do not agree with Professor Del Rio, who asserts that the Gar- 

 net is commonly trapezohedral ; though the trapezohedron in com- 

 bination with a dodecahedron is common, yet the perfect trapezohe- 

 dron is no more frequent than the perfect dodecahedron. 



But Professor Del Rio attacks the vahdity of crystallography 

 altogether. "For a student, the primary forms are no easy task, 

 which even by the professors, are often differently expressed and 

 frequently they are even doubtful; what Mr. Shepaed gives as a 

 square prism is arranged by others as a square octahedron ; and what 

 he assigns as an oblique prism is announced by some as an obhque 

 octahedron, and otherwise by others, which is not, and cannot be 

 the same to the student. I will go further in saying that the sul- 

 phuret of manganese from Transylvania and Cornwall is an hexa- 

 hedron for MoHS, and that of Mexico is a rhorabohedron for me. 

 Nay, Professor Mitscherlich infers now from his observations, 

 that every simple or composed body is able to take two different 

 forms of crystals, which is the finishing blow even to the scientific 

 classification of minerals by crystalhzation !" And then, as if out 

 of all patience with what he regards a complicated subject, he goes 

 on to say, " Therefore I propose to make as many orders as there 

 are crystals found in nature, and so the quadrangular and hexagonal 

 prisms, pointed and beveled, should constitute orders, like the reg- 

 ular hexagonal prism ; the student per se, will never find in his life- 

 time, however long, that the quartz belongs to the order of the ob- 

 tuse rhomboid." 



It is undoubtedly true that different views have been taken of the 

 connexion of the regular forms assumed by crystals, and accordingly 

 some have admitted more primary forms than others. But if each 

 writer defines and renders intelligible his own method, so as to enable 

 the student to follow him, it is enough ; whether the number be fif- 

 teen as with Brooke, (whom I have followed,) or but a single one, 



* '" If the crystal is a trapezohedron, we know it can come only from the cube, 

 the regular octahedron, or the rhombic dodecahedron." p. 77. 



