324 Mr. Shepard's reply to Prof. Del Rio. 



make greater blunders than mine, although acquainted with geome- 

 try.'' As to the Valencianite and Perikline, I believe the evidence 

 preponderates in favor of their being one and the same species ; in 

 any case, they are both distinct from Albite ; and respecting the mis- 

 takes which young students would make with the analytical system, 

 I have only to say, that without calling in question the adroitness of 

 BusTAMENTE, I should hope that persons would abstain from the 

 determination of crystals belonging to the doubly oblique prism, un- 

 til they had better acquainted themselves with the use of the go- 

 miometer, than to require the limits of error should in no case be nar- 

 rower than two degrees ! 



I did not suppose it necessary to add another character,, for the 

 distinction of Sillimanite from JefFersonite (i. e. Pyroxene), when 

 the lateral angles of the one are 92-5 and those of the other 99° ; 

 and the hardness of the former = 7*5 . . . 8*0 while that of the lat- 

 ter = 5"0 . . . 6*0. It is quite impossible to confound Kyanite, by 

 my characteristic, with the foregoing minerals or with any other spe- 

 cies of the Treatise as Prof. Del Rio appears to imagine, excepting 

 the Fibrolite of Count Bouknon which I now relinquish as a spe- 

 cies, and shall describe in my volume on Physiography as a variety 

 of Kyanite. As a rule, to be observed in the construction of a 

 Characteristic, it is conceded, that the shorter the character is, the 

 greater the facility and certainty it will afford in the distinction. 



In regard to synonymes, I adopted'the rule to give, in addition to 

 the trivial name, the systematic and the chemical names, and besides, 

 those appellations which had been bestowed upon what were gener- 

 ally regarded as forming separate species. Accordingly, under Spath- 

 ic Iron and Dolomite are found a number of names, inasmuch as 

 these species have been erroneously divided by different writers ; 

 and it appeared to me necessary to indicate to the pupil, that none 

 of these pseudo-species had been forgotten in the Characteristic. 



Of Willemite no chemical analysis was within my reach at the 

 time (1832) to inform me that this substance was a silicated carbonate 

 of zinc. Of Poonahhte, I do not, in the present state of our knowl- 

 edge respecting it, fully agree that it should be referred to Meso- 

 type ; and still less can I admit that Dysluite is Pleonaste or Spinel. 

 For Peritimous Lead Baryte and Pegamite, I know no synonymes, 

 believing them to stand for independent species. 



In the foregoing reply, I have endeavored not to pass over a single 

 remark of Prof. Del Rio, whose misapprehension of the nature of 



