212 ON THE ORIGIN, MATERIALS, COMPOSITION, 



binations, and to recrystallize without the loss of the 

 original marks of stratification, These indeed are 

 often preserved in gneiss, by the alternate interposition 

 of beds and laminae of hornblende, and by that only; 

 just as, in the watery joint deposit of sandstone and 

 shale, the latter substance is often the only indication 

 of stratification that can be procured. That such 

 recrystallization can take place in a rock which is 

 heated to a point short of actual fluidity, is proved; 

 and that strata can, in nature, lose all their indications 

 of watery deposition, while they preserve the stratified 

 shape under a new mineral form, is evinced by the 

 existence of siliceous schists beneath trap, already 

 quoted. A greater degree of heat and a longer 

 continuance of it, are all that are required to produce 

 the differences in these cases; and the fact of the fre- 

 quent interposition of hornblende schist between beds 

 of gneiss, is strongly confirmatory of the consistency 

 and truth of these views. Thus also the transition 

 of gneiss into granite becomes a phenomenon of easy 

 solution. 



Of the general Causes of Consolidation. 



I need not here terminate this view of the conso- 

 lidation of these primary rocks, by any general 

 inquiries respecting the origin of the heat or its 

 diffusion. Nothing can be said on this subject that 

 has not been said elsewhere; and whatever difficul- 

 ties may occur in attempting to apply these prin- 

 ciples rigidly to every case that may be examined, 

 it can only be said, that this theory offers a general 

 and obvious solution of the facts; and that if it 

 cannot be exactly fitted to meet every exigency, it 



