MINERALOGY, 115 
which cause the bricks made from them to burn red. At times they 
contain much lime, 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, . 7 7 : 3 . i c 3 7 : : 58.15 
Alumina, : ‘ . - . z : r 2 " 13.20 
Magnesia, é 3 5 F . . 5 7 : ‘ : 9.75 
Water, . r : 7 r 3 . : * : 5 r 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 new 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- 
