1873.] 40.3 [Genth. 



deal more than what with our knowledge of the subject, we have a right 

 to express. Yet there are so many geologists and mineralogists, who 

 have familiarized themselves with this mode of expression, that I 

 thought it an injustice to them to give merely the empirical composition. 



After having thus given the above data, the conclusions arrived at by 

 this investigation are : 



That, at the great period when the chromiferous chrysolite beds (in 

 part subsequently altered into serpentine, etc.) were deposited, a large 

 quantity of alumina was separated which formed beds of corundum ; 



That, this corundum has subsequently been acted upon and thus been 

 changed into various minerals, such as spinel, fibrolite, cyanite, and per- 

 haps into some varieties of feldspar, also into tourmaline, damourite, 

 chlorite and margarite ; 



That, a part of the iiroducts of the alteration of corundum still exists 

 in the form of large beds of mica-(damourite) and chlorite-slates or 

 schists ; 



That, another part has been farther altered and converted into other 

 minerals and rocks, such as pyrophyllite, paragonite, beauxite, lazulite, 

 etc. 



The question lias often been asked me, how I could explain these -won- 

 derful changes which have taken place with a substance so absolutely 

 insoluble as corundum '? My answer is that I know nothing about it. I 

 have in this whole investigation carefully avoided making any statements 

 which are not based upon undeniable facts ; in a few instances only, 

 where the facts were very strong in my favor, I have allowed myself to 

 judge from analogy. 



Mr. S. P. Sharpless is probably correct in his supposition that corun- 

 dum has been altered into lesleyite and pattersonite by the action upon 

 it of water containing alcaline silicates. Such a view is very plausible, 

 especially if we add an elevated temperature and great pressure. I have 

 ried a number of experiments in this direction. I have put corundum 

 reduced to an impalpable powder, and subsequently boiled out with 

 chlorhydric acid and washed with water, into a glass tube with a solution 

 of potassic silicate, and after sealing it have exposed it to a temperature, 

 which was gradually increased to about 2o0° C. With one exception, all 

 my tubes burst before the alcaline silicate had time to act upon the 

 corundum. In this one case the tube stood for about three days and 

 nights, before it exploded. The scales of the mineral substance, which 

 came from the tube were carefully collected, washed out and then treated 

 with dilute chlorhydric acid and evaporated to dryness, the residue 

 moistened with chlorhydric acid, the mass extracted by water. The clear 

 liquid gave with ammoniac hydrate a trace of a flocculent precipitate, which 

 appeared to be alumina. The quantity was too small, however, to place 

 any value upon this experiment. It may be well to mention in this con- 

 nection that under pressure and reduced to a fine powder, corundum dis- 



