GEOLOGY OF CENTRAL INDIA. 31 



qualified to give a particular name to this class of rocks, and in describ- 

 ing them, I shall merely state their composition; as for instance, "a 

 granitic rock composed principally of reddish colored felspar, with minute 

 scales of mica interspersed through its substance"— stating the relative 

 proportions of the ingredients to each other, &c. &c. Several rocks com- 

 posed of felspar and quartz, and which were alluded to above, shall also 

 be placed under this head, and these are either large or small grained, &c. 

 The term granitic porphyry might, perhaps, be applied to the latter. 



Gneiss. — Gneiss, as it commonly occurs, requires no definition, and 

 the only other varieties which I have observed in this district are^First. 

 A gneiss in which the mica is replaced by hornblende, and to which 

 I have applied the name of sienitic gniess : — and Second. A gniess in which 

 the mica appears to be replaced by chlorite. To this last, the term 

 chloritic gniess may be applied. 



Quartz Rock. — I have, perhaps, placed a greater variety of rocks 

 under this head than I ought to have done. The immense beds of quartz 

 rock, however, which present themselves in this district, form a very 

 striking feature in its Geology. From the pure white semi-transparent 

 quartz, to the more slaty varieties, where it passes into micaceous and 

 argillaceous schists, there is a regular gradation observed, and I cannot help 

 thinking, that one general name ought to be applied to the whole series. 

 It occurs either stratified or unstratified. The former, perhaps, where it 

 passes into the argillaceous schists, ought to be named flinty slate. I 

 prefer, however, retaining the name of quartz rock, as the other might 

 lead us to confound it with a more recent formation, in which the flinty 

 structure, as commonly understood, is a characteristic feature. When 

 any individual of this class passes into any particular rock, the circum- 

 stance shall be mentioned, while the more compact varieties of argillaceous 



