XII INTRODUCTION. 



however, from the external constitution, the predominant 

 central substances are iron and silex, or the metal of silex. 

 For silex itself, as already explained, is frequently a new pro- 

 duction, found in the straw of graminous plants and the 

 bark of the bamboo. Nay, pebbles of quartz are found in 

 the bamboo itself 5 and often of the size of a pea in the eggs 

 of the ostrich *. 



Ferrara's Ferrara's able account of the volcanoes of Sicily has also 

 opened some new geological ideas. In one passage he thus 

 expresses himself: " The natural philosopher who has ex- 

 plained the formation, that is, the condensation and consoli- 

 dation, of the globe, and the inequalities of its surface, as 

 being produced by operations arising from an innate power 

 in matter, from a power most generally diffused, from a 

 power to which nature has put no limits of action upon 

 the spot which we inhabit, but at the same time destined 

 to bind all the parts of the universe together, in order 

 to form a well-regulated whole 5 in a word, by gravita- 

 tion: it would seem that he approaches nearer the veri- 

 similitude of causes : he does not leave the earth in order to 

 explain the facts which are found in it ; he has not created 

 extraordinary powers j but has attributed all the phenomena 

 to agencies which still operate, although upon another scale, 

 but which would renew the same phenomena, if they were 

 conducted under the same circumstances. From what I have 

 said it may be understood that my opinion is with those who 

 suppose that this globe was formed of materials which, being 

 first diffused in a fluid, were thence deposited successively, 

 and which occasioned all the disorder which we observe on 

 the surface by the sinking of some parts, while others remain 

 elevated in their original site and level. Burnet, who not 

 long since started this grand and perhaps ancient idea, has 



* See Barrow's Cape of Good Hope. Breislak, ii. 205, may be consulted 

 for the dissolution of silex, which he says is effected by water impregnated with 

 caloric, soda, and sulphur in a state of vapour. Kirwan, i. 155, says, oxyd of 

 iron with microcosmic salt yields a pale green glass, that is, a siliceous substance. 



