M. Keilhau's Theory of Granite and other Rocks. 267 



for returning to those other ideas, which, not merely one, but a 

 large number of facts have proved to be faulty and unsatisfac- 

 tory. The experience connected with the old theories ought to 

 render us cautious respecting our expectations of the new one ; 

 all that we can hope is to bring an idea upon the path as some- 

 what more productive, somewhat more correct, than those with 

 which we have hitherto endeavoured to assist ourselves. I must 

 also remark, in regard to the proposed theory of the origin of 

 the massive rocks, that it must always be kept in mind that it 

 by no means pretends to be without exception available ; — to 

 which of these rocks it is to be applied is a problem which re- 

 mains yet to be more exactly determined. When we were con- 

 sidering the crystalline masses occurring in Vesuvius, which, so 

 far as we are informed by descriptions, have completely the 

 forms of our greenstone veins, we did not doubt of their having 

 resulted from erupted lava ; we considered it further as ex- 

 tremely probable that a number of masses having other forms 

 likewise came from the interior in a melted condition, and by 

 slow consolidation and great pressure assumed even a granite- 

 like nature. Thus far we have granted, and thus far we shall 

 concede to volcanism all its just rights; and the views now de- 

 veloped only claim to be placed at the side of the other theory. 

 More extended investigation will perhaps shew that, instead of 

 being opposed to the volcanic system, these views, on the con- 

 trary, approach to a union with it. If metamorphoses take 

 place, in general, in the way we have imagined, there is then 

 no ground for assuming that merely original Neptunian, and 

 not also volcanic rocks, were subjected to them. But a more 

 intimate union of ideas of the pyrogenetic formation of the 

 massive rocks, and ideas of their production by metamorphoses, 

 may be imagined ; so that both opinions may possibly be in- 

 cluded under one and the same higher conception. One has 

 merely to examine a little more attentively what takes place 

 when a liquid mass becomes solidified, — for example, when it 

 becomes granite. If we attempt to take the subject into consi- 

 deration in somewhat more than a superficial manner, we shall 

 find ourselves obliged to go into ideas not disagreeing with that 

 theory to which our previous examinations have led us ; and 

 processes of transition of amorphous and homogeneous masses, 



