312 



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



Akt. XVIII. — Reply to " Observations on the Treatise of Miner- 

 alogy of Mr. C. U. Shepard, by Andres Del Rio, Professor 

 of Mineralogy in the School of Mines of Mexico ; Pres. of the 

 Geological Soc. of Penn. &fc. (Read before the Geol. Soc. of 

 Penn., June, 1834," and published in the Transactions of that so- 

 ciety August, 1834.) By Charles U. Shepakd. 



Prof. Del Rio, in presenting to the Geological Society of Penn- 

 sylvania a translation of the classes and orders of Bkeithaupt's 

 Characteristic, takes occasion to remark upon its superiority over 

 that contained in ray Treatise on Mineralogy, and which, unlike the 

 Characteristics of Mohs and Breithaupt, is appHed to an artificial 

 system. As his observations are of a general nature, and as he has 

 omitted giving the reader a fair opportunity of judging of the mat- 

 ter through the aid of an example from each, by performing the task 

 myself, I may be able to place the subject in a stronger light; al- 

 though I believe the experiment will prove that the advantage in 

 facility, on wliich the question turns, will he quite on the other side. 

 And without attempting unduly to favor myself by the selection, I 

 will take a species which offers as nearly as possible, similar difficul- 

 ties in both systems. Let the substance for determination be, either 

 crystallized in the form of a right square prism, cleavable parallel 

 to its sides ; or massive with large individuals ; or finally massive in 

 small, closely connected individuals. Sp. Gr.=4'2 . . . 4*4. Hard- 

 ness=8-0 . . . 9-0 of Breithaupt's scale, or=6'5 of Mohs. Lus- 

 tre metallic-adamantine, (common according to Breith aupt) . Col- 

 or reddish brown. Streak pale brown. 



Characteristic of Bkeithaupt. 



To determine the Class. 

 1. Class. Salts. 

 Common lustre. 



H. 0-25 . . . 4-50. But the 

 hardness of the mineral sought be- 

 ing 8-0 . . . 9*0, it is excluded. 



n. Class. 

 Common lustre. 

 H. 0-25 . . . 120. 

 G. 1-8 ... 8-1. 



Stones. 



My Characteristic. 



To determine the Class. 

 1. Class. Crystallized Miner- 

 als. 



Minerals crystallized, (i. e. in 

 regular forms.) 



If the mineral sought is a crys- 

 tal, it falls within this class. 



n. Class. Semi-crystallized 

 Minerals, (i. e. massive miner- 

 als in large, easily cleavable indi- 

 viduals.) 



