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NATURAL HISTORY OF SILEX.

SIjLEX,

PART LVIII.

SECT. I.

NATURAL HISTORY OF SILEX.

CJlLEX, or siliceous earth, is the principal constituent part of avery great number of the compound earths and stones formingthe immense mass of the solid nucleus of the globe. It is thebasis of almost all the scintillating stones, such as flint, rockcrystal, quartz, agate, calcedony, jasper, tsfc. The sand of ri-vers and of the sea-shore, chiefly consist of it. It is depositedin vegetable substances forming petrified wood, 8tc. It is like-wise precipitated from certain springs in a stalactitical form. Ithas been discovered in several waters in a state of solution, andis found in many plants, particularly grasses and equisetums.Professor Davy has proved that it forms a part of the epidermisof these vegetables. It is never met with absolutely pure innature.