MINERALOGY. 1 1 5 



which cause the bricks made from them to burn red. At times they 

 contain much hme, when they are called marl. 



Kaolin, when pure, is white, and often flaky. When clay is consoli- 

 dated, it forms beds of argillite, and this is the first stage in metamor- 

 phism. The beginning of the change is marked by the production of 

 an imperfect schistose structure, a loss of a part of the water and of the 

 soapy feel. 



Clays are not merely variable on account of their composite nature; 

 but a large number of apparently pure and homogeneous products have 

 been analyzed, and a number of species established as the result. Amor- 

 phous clay-like products, very different in appearance and physical prop- 

 erties, are found. They are, as a rule, kaolin in different states of con- 

 solidation, but one most peculiar product, called mountain cork, is found 

 at Franconia. It is extremely light, though apparently firm and com- 

 pact. It is made of the finest microscopic fibres, so interlaced as to 

 make the mass very tough and hard to tear, though it cuts with a knife 

 like cork. It floats lightly on water, but it rapidly absorbs water, and 

 then sinks. Its weight is about equal to that of cork, and its whole 

 appearance immediately suggests the name by which it goes. Similar 

 products to this, and which are called by the same name, are composed 

 of hornblende; but this substance, which I have analyzed, and which 

 was furnished to Prof. Brush by Mr. Pierce, of Providence, who obtained 

 it from our state, gave as the result of analysis, — 



Silica 58.15 



Alumina, 13-20 



Magnesia, 9-75 



Water, 18.68 



99.78 



The same product was analyzed by Mr. Calder, of Providence, and his 

 results were not widely different from mine ; but every new analysis that 

 he made gave him n^v results. Hence, as no two analyses can be 

 made to agree, it is plain that the substance is not homogeneous, and 

 that it is merely a hydrated and altered asbestus (hornblende). It fuses 

 without difficulty before the blow-pipe, and its composition is such as to 

 make this conclusion tolerably certain. This product has excited consid- 



