1845.] Notes on the South Mahratta Country, fyc. 285 



of jasper rock,* viz. " where strata of quartz rock, containing much 

 felspar or clay occur in contact with granite, they pass into jasper 

 if the clay abounds ; while in other places they are converted into 

 chert if less of that earth is present ; or, if pure, are rendered perfectly 

 crystalline." 



With regard to the classification of jaspideous rocks associated with 

 the metamorphic schists of S. India, it is clear they either belong to 

 the jasper rocks, or silicious schists of McCulloch, both of which, 

 however, I have reason to think, pass occasionally into each other. 

 Both occur in strata among the metamorphic rocks ; jasper sometimes 

 forming hills in Siberia and Norway, and it is seen in Scotland and the 

 Appennines imbedded in micaceous and argillaceous schists. 



The difficulty that sometimes exists of distinguishing these two rocks 

 has not escaped the notice of McCulloch, who thus remarks: " Jasper 

 presents a few modifications of internal structure which require notice. 

 It sometimes gives indications of a spheroidal concretionary dis- 

 position, more or less perfect, and resembling that which, under cir- 

 cumstances of a similar nature, occurs in chert and silicious schist. In 

 the same way, it sometimes possesses a laminar structure, and in this 

 also it approximates to the silicious schists. It is easy to see how 

 from similarity of origin, connexion and composition, it may be thus 

 a matter of doubt to which of those two rocks any given specimen 

 or bed should be referred. The well known striped and spotted 

 jaspers owe their appearance to the two structures above-mentioned, 

 and occasionally the two are combined in the same specimen." 



There is however a perhaps somewhat empirical distinction drawn 

 by some geologists between these two classes of rocks, founded upon 

 the supposed less stratified character of jasper, its intrusion into 

 other rocks in the state of veins, and its association with trap rocks, 

 which I will avail myself of to place, pro-tempore, the jaspideous 

 rocks of Southern India among the silicious schists ; from their, in ge- 

 neral, decidedly stratified character, particularly those of the Southern 

 Marhatta country, which pass into the associated schists, and preserve a 

 conformable dip and direction. The petrographical characters of the 

 Marhatta beds, varying according to the degree of induration, and 



* Classification of Rocks, pp. 546-47. 



