VON BUCK ON GRANITE. 127 



and it follows from this view that the granite thus lifted up from 

 below cannot be considered as any kind of lava, or as a fluid 

 substance filling up fissures from above, but that it possessed a 

 certain consistency which in most cases was far removed from the 

 condition of fluidity ; and indeed the beautiful and regular external 

 form which the rock assumes, renders any other assumption impos- 

 sible. This degree of hardness or consistency, however, which the 

 Plutonic rocks must generally have possessed at the time of their 

 elevation into mountain- chains, does not exclude a certain degree 

 of plasticity, a condition without which this kind of elevation can 

 scarcely be conceived. 



If, however, granitic masses are forced upwards in thick ellip- 

 soidal bubbles by forces acting from beneath, it is also conceivable 

 that such masses should neither appear in a fluid state nor break 

 through the surface in detached fragments and needles, but present 

 themselves in an arched or vaulted condition, the vault being 

 larger and more perfect in proportion to the force acting and the 

 extent of the surface acted on. 



Now on examining the " sea of rocks" upon the Brocken some- 

 what more carefully, we shall observe a striking relation of the 

 blocks amongst each other. They readily arrange themselves into 

 a widely-extended cover of the granitic vault, and the separate 

 blocks seem as if their projecting and re-entering angles might be- 

 long to one another. Unless, indeed, this were the case, one cannot 

 imagine how the distant view of the Brocken could be so perfectly 

 regular that a small house upon the top should be a conspicuous 

 object. The blocks remain in their original position, for they cer- 

 tainly have not been brought here from a distance, nor can any 

 decay of the surface have produced them, for a decay that could 

 have effected this would have destroyed the marks of any relation 

 which the blocks bear to one another ; nor, lastly, can any violent 

 disruption have acted, since such a disturbance must have altered 

 the regular form of the mountain. The phenomenon is, I maintain, 

 the inevitable result of the contraction of the upper dome-shaped 

 surface, and the circumstances under which it was pushed up from 

 below. If this is the case, we may understand how these seas of 

 rocks may be common with regard to granite, and rare in other 

 formations, since the granite, when it appears, offers a fresh sur- 

 face ; while other rocks, elevated by it, have had their surface long 

 exposed. 



If the existence of a similar contraction to this in the interior of 

 granitic ellipsoids is admitted, an internal structure becomes un- 

 veiled, which demands great attention. That which we discover in 

 the apparently disconnected blocks of the sea of rocks, a splitting up, 

 namely, into conchoidal surfaces, exists also in the interior, and 

 appears in a very singular manner. Large and compact concentric 

 layers are seen, and the form of the circumference of the moun- 

 tain is repeated by such concentric layers, gradually diminishing 

 in size, until, at last, the innermost nucleus appears to be cylindrical, 

 a singular arrangement, which may be seen in granitic bosses of 



