﻿272 LI. A. Wheeler — Artificial Lead Silicate. 



meat, will be made to the full extent that any newly ob- 

 tained information may direct. It is recognized, too, that 

 nature's methods are multiple and complex, similar results pro- 

 ceeding from very different causes ; and it is not designed to 

 say that the theory covers all occurrences of ferruginous rocks 

 in the Lake Superior country. For instance, we have found 

 rocks composed of quartz, actinolite and magnetite to have 

 been derived from the alteration of an olivine-gabbro of the 

 Keweenaw series. These actinolitic rocks are very different in 

 habit, however, from the actinolitic magnetite-schists above 

 alluded to, but still the existence of such an alteration admon- 

 ishes us that similar changes may have taken place more 

 widely than is now suspected. 



Nevertheless it is thought that in its main features the theory 

 now presented will stand. It has this in its favor, at least, 

 that its author has not been impelled to it by any preconceived 

 notions — such ideas as he had having been much more opposed 

 to such an hypothesis than in its favor — but has been led to it 

 very gradually during the growth of an experience with these 

 singular substances, which, in extent of territory covered, and in 

 abundance of material examined, probably no other geologist 

 has had the opportunity to obtain. 



Washington, D. C, March, 1886. 



Art. XXX. — Further Notes on the Artificial Lead Silicate from 

 Bonne Terre, Mo. ; by H. A. Wheeler. 



In the number of this Journal for August, 1885, there are 

 some crystallographic determinations and analyses of both the 

 crystallized and massive types of this artificial mineral from 

 the Desloge Lead Co., of Bonne Terre, Mo. ; by E. S. Dana 

 and S. L. Penfleld. Since then I have had an opportunity to 

 examine some specimens in the metallurgical collection of 

 Washington University of this interesting material. The 

 metallurgist of the Desloge Co., Mr. J. T. Monell, who for- 

 warded the above specimens, informs me that the crystals were 

 found directly under the hearth of an old Freiberg or reverb- 

 eratory roasting furnace, close to the fire-bridge. The ore of 

 this company, which is exclusively galena, is all treated, pre- 

 paratory to smelting in a water-jacket furnace, to a preliminary 

 roasting. Silica, to the extent of 10 or 12 per cent, is added to 

 the roasting charge, and the heat is carried sufficiently high, at 

 the latter part of the roasting, to agglomerate and melt the 

 charge by the time it reaches the fire-bridge. It was directly 

 •under this fusion hearth of the furnace that the crystals of the 



