Genth.] -iUb [Sep. 19,1873. 



solves with considerable facility in dilute sulphuric acid, as I have 

 already stated above. 



I hope that the time may soon arrive when we shall have a clwr 

 insight into the alterations of corundum, which I have above described. 

 At present we have no facts upon which a tenable theory could be built. 



And this finishes my task. I have devoted to it my leisure hours for 

 over two years. Nobody can be more aware of the many imperfections 

 of this investigation, but I hope that it will be taken into consideration 

 that I have labored under very great disadvantages. I had for consulta- 

 tion neither a collection to compare my specimens with those from other 

 parts of the world, nor a library of sufficient completeness. All that I 

 have done, I have done with my own labor and the assistance of many 

 kind friends, to whom I am under great obligations ; of the many who 

 helped with specimens, etc., I will especially mention Rev. Dr. E. R. 

 Beadle, Prof. G. J. Brush, Dr. Isaac Lea, Dr. Joseph Leidy, Rev. C. D. 

 Smith, of Franklin, North Carolina ; Prof. E. A. Smith, of Tuscaloosa, 

 Alabama, and Col. Joseph Wiilcox ; the greatest gratitude I owe to my 

 assistants, Dr. Geo. A. Koenig and Thos. M. Chatard, S. B., for the 

 many valuable analyses which they made, and which alone have enabled 

 me to finish this work in this comparatively short time. 



University of Pennsylvania, August 18, 1873. 



Postscript. 



Since writing the above, an article has appeared in the September 

 number of the American Journal of Science and Arts, entitled "Notes 

 on the Corundum of North Carolina, etc., by J. Lawrence Smith, Louis- 

 ville, Kentucky," which contains analyses of a few species, discussed in 

 my paper. 



There are a few points to which I wish to call attention. 



Under "zoisite," Dr. Smith gives analyses of two minerals, which, in 

 my opinion, do not belong to this species. The "light green" analyzed 

 by Tho. M. Chatard and described as Smaragdite(?) (Kokscharoffite), is 

 probably an aluminous hornblende (?), the black variety is evidently the 

 same mineral, containing, however, as proved by Dr. Smith's analysis, 

 a part of the alumina replaced by ferric oxide. The zoisite from Culla- 

 kenee is always white with only a slight grayish or greenish tint. 



The granular " andesiie " gives, according to his analysis, the oxygen 

 ratio 0.85 : 3 : 9.09, which is very near = 1:3:9, placing this mine- 

 ral, like that from Chester, Massachusetts, under oligoclase. 



Philadelphia, August 28, 1873. 



