Sheparcfs Treatise on Mineralogy. 175 



mineralogists, I trust that you will not allow this possible error, 

 to have too much weight in deciding either against the principles 

 of the treatise, or the general success with which they are re- 

 duced to practice. 



Chathainite was put forth as new, not for chemical reasons, as 

 supposed, but simply from a difference of specific gravity between 

 the Chatham mineral and white nickel. I may also add, that a 

 degree of negative evidence still weighs in my own mind in favor 

 of the correctness of the opinion, arising from the fact, that the 

 mine though explored for months for this ore, has not as yet af- 

 forded a single specimen which shows the crystalline form to be 

 identical with that of white nickel, as might have been expected, 

 provided the relationship you suppose, exists. 



In conclusion I have only to remark, that I regret taking up 

 the pages of this Journal, devoted as it is to the records of Ameri- 

 can science, with the present rejoinder ; but the unfavorable posi- 

 tion in which your criticisms were calculated to place my trea- 

 tise, appeared to leave me no alternative on the occasion, either 

 as I valued my scientific reputation, or those systematic views in 

 mineralogy, which have commended themselves so strongly to 

 my understanding. 



2. Various Mineralogical Notices. 



1. Quincite. — I find the variety with a conchoidal fracture to 

 possess a hardness=6-0, and a gravity, from 2*05 . . . 2-30. 



2. Lincolnite. — It is suggested by the editors of this Journal, 

 (in the last number, p. 416,) that the angle 116° 45' ... 117° 15', 

 obtained by me for the inclination of the lateral faces of the 

 Lincolnite, is simply that belonging to a secondary form of Heu- 

 landite, in which the plane replacing the acute lateral edges, is 

 so far produced as to extinguish the shorter faces of the primary, 

 since such a supposition only has to account for an error of 2° 

 15' ... 2° 45', which it is supposed may have arisen from the disad- 

 vantageous method I was forced to adopt in determining my an- 

 gles. To show that this suggestion is not very probable, I have 

 to state, that I have repeated my measurements on another crys- 

 tal, and found that the mean of five successive trials, gave 117° 

 08' 06" (the extreme being 1 17° and 117° 24'. ) By the same mode 

 of trial, I found the larger angles of a genuine Heulandite to be 

 130° 15', and the angles supposed to be identical with that de- 

 termined by me for Lincoluite, 113° 38'. 



