Jackson.] 172 [December 3, 



December 3, 1869. 

 The President in the chair. Sixteen persons present. 



Dr. C. T. Jackson presented, in the name of Mr. Daniel 

 McCain, specimens of native carbonate of magnesia from 

 Greece, California, Maryland and Kansas. 



That from Greece contains ninety nine per cent, of pure carbonate 

 of magnesia, the rest, or one per cent , being siliceous matter. 



The California specimen came from Alameda County, thirty six 

 miles from San Francisco. It is of the same degree of purity as that 

 from Greece. 



The Maryland sample is rich enough for use, and contains seventy 

 nine and two tenths per cent, of carbonate of magnesia. 



The Kansas sample is very poor, containing but eight per cent, 

 of carbonate of magnesia. 



These minerals are used by the Union Stone Company in making 

 calcined magnesia, which is one of the ingredients of their artifi- 

 cial stone, serving, when combined with chloride of magnesium, as 

 the binding material. 



Dr. Jackson gave a # detailed account of the method of making the 

 artificial stones, and of casting bas reliefs, busts and ornamental 

 mouldings. He said the processes had been so improved that now 

 artificial grindstones made of quartz-sand and of emery, had been 

 constructed, which were as solid and durable as any natural stone. 

 The emery wdieels made of these materials are vastly better than 

 those made with a paste of vulcanized india rubber, since they do 

 not glaze, but wear away in such a manner as to always expose 

 fresh particles of emery. He regarded this new manufacture as of 

 great value for architecture and the mechanic arts, and as showing 

 the importance of the mineral native carbonate of magnesia, which 

 had been before used only for the manufacture of epsom salts, of 

 which a limited supply only is wanted. 



Professor N. S. Shaler offered some remarks on the rela- 

 tions of the rocks in the vicinity of Boston, of which the 

 following is an abstract : — 



The association of the several different sets of beds wdiich are ex- 

 posed in the neighborhood of Boston, is very difficult to determine 



