CHAP. XL. 



; 

 Jasper, Siliceous Schist, Chert. 



As these three substances are produced by the casual 

 influence of heat on certain ordinary strata of aqueous 

 origin, occurring also both among the primary and 

 secondary, I have, for the first time, introduced them 

 into the system of rocks, as having been both neglected 

 and misunderstood ; while, by thus uniting them, they 

 will best illustrate each other, as well as the philo- 

 sophy of Geology. 



Onr information respecting Jasper is very imperfect, 

 as it has not received much attention from geologists, 

 by whom also it has most commonly been misappre- 

 hended; though mineralogy is not deficient in descrip- 

 tions of its varieties. As yet it has not been found 

 occupying large spaces, or forming mountain masses ; 

 though carelessly said to occur in this manner in 

 Siberia, where, if it has been thus conceived to possess a 

 considerable extent, the leading mass has probably 

 Ijeen some other rock, of which certain portions had 

 assumed its characters. In this manner it does ac- 

 tually occur in Siberia, and in the Apennines, in large 

 masses imbedded among the primary strata ; as also 

 in Scotland, between Blairgowrie and Stonehaven, but 

 on a very limited scale. According to Soulavie, it 

 is found, in France, between granite and basalt ; a 

 position, which, according to the view here entertained 

 of its origin, is as instructive as it is to be expected. 

 Its peculiar situation in the Apennines, described by 

 Brongniart, ,was already noticed. 



Under these circumstances, I have been unable to 

 derive from the works of authors, except in the above- 

 mentioned instances, any information that could be 



VOL. II. T 



