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I.— NATURE and FORMATION of FLINT. 



Silica, or the oxide of silicon, enters largely into the composition 

 of granite, felspar, and sandstone ; and occurs in a pure 

 state as quartz and as silex or flint. Bands of impure flint, very 

 common in mountain limestone, and sometimes found in the 

 chalk, are called chert. 



Certain hot springs and geysers, like those in Iceland and New 

 Zealand, contain in solution large quantities of silica in combin- 

 ation with soda, lime, magnesia and iron. 



When these heated solutions cool, they deposit silicates on any 

 substance with which they come into contact ; so that animal or 

 vegetable tissues immersed in these waters may become petrified 

 in their deepest fibres. 



The banks of Lake Taupo, says Mr. Martin, who has lately 

 visited it, are perforated with thousands of springs which form 

 cooking-places for the Maoris. Every hut has its natural boiler 

 in which baskets of potatoes, fish or other food are suspended 

 until ready for table ; while, over some . of the hottest portions of 

 the ground, large slabs of stone are placed, on which, covered by 

 moist grass, bread is baked. 



Passing through this district, Mr. Martin came upon a spacious 

 plateau of silica which reverberated beneath his tread. The 

 temperature of its surface was over ioo°R ; and a large opening 

 revealed the fact that he was walking on a crust of unknown 

 strength and thickness over a huge basin of boiling water. 

 Numerous smaller springs, supersaturated solutions of silica, 

 formed very beautiful incrustations in a short time, and articles 

 dipped into them were speedily covered with a soft and delicate 

 deposit resembling hoar-frost. Taking a bath in a neighbouring 

 pool, in a few minutes one's skin was covered with a fine silicious 

 coating of exquisite smoothness. 



It has been ascertained by analysis that the silicates contained 

 in these waters vary in quantity from 71 grains in a gallon to 

 3 grains in a gallon. 



