THEORY OF THE EARTH. 451 



Yet wherecver I have suggested this possibility, or 

 probability, in any case, even in that vexations one of 

 the red marl, let this never be forgotten. The moun- 

 tain limestone contains shells ; and shells are oblite- 

 rated, even by the passage of trap veins, as I have 

 amply proved. Therefore such heat, if it did act in any 

 case, did not act as it assuredly has done on the primary 

 strata, extensively, or universally. And it might have 

 affected one deposit, such as the red marl, without in- 

 volving all above, or even below: since the non-con- 

 ducting property of rocks, so much overlooked by theo- 

 rists, will account for this, and much more. The whole 

 solid portion of the globe needs not have been affected 

 by every effusion of ignited and fluid rock. And any 

 one who will reflect, for himself, on this, as on many 

 other subjects, here stated so briefly as to demand deep 

 reflection, will comprehend what I cowld not have fully 

 explained without occupying an entire volume. I know 

 not that I have acted right in suppressing that volume, 

 and thus condensing such a mass of thought. But it 

 will give readers the opportunity of thinking: of that, 

 by which information becomes knowledge. 



With respect to the primary strata, their present 

 nature and successions will indicate, with no great 

 difficulty, what those where when in their first con- 

 dition. And the nature of the original materials, 

 with the degree and mode of the heat to which they 

 have been exposed, will serve to account, as well as 

 we can now expect, for their differences. 



Gneiss, when granitic, is, thus, an uneffused granite: 

 as it approaches nearer to micaceous schist, the same 

 theory serves for both, and also for the analogous 

 schists ; or the fusion has been less perfect or less du- 

 rable : while, in each case, the parallelism of the mica, 

 like the laminar arrangement of the felspar, and the 



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