310 ON THE IGNEOUS METAMORPHOSIS [Ch. XIV. 



It is time, however, to turn our attention to the primary 

 rocks ; in order to enquire whether the slates of this class 

 owe their crystalline condition, and their exemption from 

 organic remains, to the influence of granite, and other un- 

 stratified rocks, in a state of ignition. " According to these 

 (Plutonic) views," says Lyell, "gneiss and mica-schist may 

 be nothing more than micaceous and argillaceous sandstones, 

 altered by heat ; and, certainly, in the mode of their stra- 

 tification and lamination, they correspond most exactly. 

 Granular quartz may have been derived from siliceous sand- 

 stone, compact quartz from the same. Clay-slate may be 

 altered shale ; and shale appears to be clay that has been 

 subject to great pressure."* Without, however, following 

 this exposition farther, we will proceed to show that the 

 changes which the sedimentary strata exhibit, next trap, are 

 not perfectly similar to the condition of the primary slates ; 

 thus furnishing an additional argument against the analogy 

 which is supposed to exist between the primary and fossili- 

 ferous strata. 



It has been attempted to show, in a former chapter, that 

 the lamination or structure of these rocks, though often 

 similar, does not depend on stratification, or rather on the 

 mode in which they have been deposited ; and in the begin- 

 ning of this chapter, it has been advanced, that the transition 

 between the primary slates and the adjacent secondary strata 

 does not infallibly prove that they belong to one and the 

 same epoch. Still, however, even considering these topics to 

 be disposed of, the question whether the primary strata are 

 altered rocks, involves some other important considerations i 

 and none of greater moment, than whether granite has 

 actually been in a state of igneous fusion since the formation 

 of the primary slates; for the whole question necessarily 

 depends on this point, which we think has not been satis- 

 factorily established, but which for the present may be 

 conceded. 



* Principles of Geology, vol. iii. p. 373. 



