172 Shepard's Treatise on Mineralogy. 



ity," which obliges me to attempt their vindication from this new 

 attack against their sufficiency ; for it may be recollected that the 

 first edition of the treatise brought down upon my characteristic 

 numerous objections from Prof. Del Kio, which I endeavored to 

 controvert in Vol. xxvii, p. 312, of this Journal. In proof of 

 your charge you merely cite the specific character of apatite, fol- 

 lowing it up by this single observation, "This is all the informa- 

 tion which the author thinks necessary to enable the learner to 

 determine this species." But in making this charge, you over- 

 look the characters I have also given, in their proper places, for 

 determining the class, order, and section, respectively, to which 

 apatite belongs. You must be aware that my characteristic is 

 no more liable to the charge made, than would that in botany be, 

 because the usual specific character for the Cornus Canadensis 

 (which is "herbaceous, leaves at the top whorled, veiny, involu- 

 cres ovate, acuminate, fruit globose") is insufficient for its deter- 

 mination. In both cases it is alike required that the characters 

 for the higher ideas in the system be first availed of, beginning 

 with the most comprehensive, and descending, gradaiim, to the 

 species. 



Before then you can affirm that my tables for determination 

 are insufficient, you must show that a student with an individual 

 of apatite in hand, after the use of the appropriate means for learn- 

 ing its form, hardness, and gravity, cannot by the rules given re- 

 fer it to its appropriate species. When this is done, you will 

 have demonstrated the failure of my characteristic in respect to 

 one of its 343 species.* 



* I should be less anxious to viodinale the practical part of the treatise from the 

 force of your objection, did I not suppose it to be the most original feature of the 

 production. Indeed, it was the construction of a characteristic analogous to those 

 employed in zoology and botany, which first led me to become a writer on this 

 science ; and I may perhaps be allowed here to state the peculiarity of my method, 

 as the subject is one of admitted importance, and respecting which my first re- 

 viewer (Del Rio) remarked — " the mere attempt to solve a difficult problem is 

 in itself worthy of praise, although the method be complicated, because it can be 

 subsequently simplified." This method has been greatly modified in the second 

 edition, although its principal feature is still retained, which is that of distributing 

 minerals into classes and orders on some general grounds, and then arranging the 

 contents of the orders in a series depending on hardness, placing the softest first 

 and ending with the hardest species; the hardness of each being given by the 

 scale of MoHS in acolumn immediately to the right of the names for each species 

 in the list. Adjoining this and on the right again, is appended a column contain- 

 ing the gravities of the species; and whenever it is supposed that these two prop- 



