100 M. Keilhau's Theory ofGranitCy and other Rocks, 



nate, at least entirely, from the very points where the new sub- 

 stances were formed; but that they were conveyed to these points. 

 We are, therefore, obliged to admit certain attractions, as the ac- 

 tive moving agent which transported matter to such points, 

 and also a power which prepared and formed the requisite 

 space for the matter that was collected at these places. Ex- 

 amples often come before our eyes of such occurrences in pasty 

 media, where a chemical substance is formed at certain points ; 

 but examples are not awanting where the medium was a com- 

 pletely solid, rigid mass, and where the same phenomenon has 

 taken place. I shall only allude to the occurrence of mellite 

 or honey-stone, in imbedded crystals in brown coal. Really 

 it appears to me, that the difficulties are not much greater in 

 understanding this phenomenon in an entirely solid medium, 

 than in a pasty one, for the latter is certainly not much more 

 permeable, or much more suited for the movement of fine fluids 

 than the former, and we cannot more easily see how the shoot- 

 ing out of crystals can push aside the pasty mass, than how the 

 compact mass is forced lo make room for the crystals. But we 

 cannot proceed farther, than merely thus to convey a general 

 impression of the phenomena ; this will at least preserve us 

 from untimely and wild attempts to give explanations of oc- 

 currences, regarding which more cannot in the mean time be 

 demanded than a simple glance at the facts as they are exhi- 

 bited in nature. Thus, I do not perceive what idea can be 

 formed, for example, respecting the occurrence of chiastolite 

 in clay- slate ; or of crystals of felspar in limestone, or in 

 quartzose sandstone ; or of so many other similar developments 

 of crystals, if we do not adhere simply to the notions spring- 

 ing from the unfettered conclusions presented by nature. 



From the same considerations, and generally from those re- 

 sulting from the facts regarding the changes which take place 

 in solid bodies, we have now, as 1 trust, to form our ideas of 

 the formation of granite, and the other massive rocks of which 

 we are treating. We must return to- the same source when 

 we consider the origin of gneiss, mica-slate, or generally of the 

 crystalline slates ; nay, the same leading idea will at last be 

 made to apply to clay. slate and other crystalline rocks ; for 

 when well considered, although their origin has hitherto at. 



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