128 GEOLOGICAL MEMOIRS. 



small circumference, but which, of course, cannot be followed in a 

 large mountain, such as the Brocken. This remarkable concentric 

 arrangement has often been mistaken for stratification ; and this is 

 not extraordinary, since we can generally see so little below the 

 surface of the actual structure. 



It is not, however, the case that every great granitic mass is a 

 single ellipsoid in concentric layers. More frequently, and, indeed, 

 generally, when the extent of the granite is considerable, several 

 such systems run into one another, and smaller ones are included 

 within the larger. Near the Brocken several surrounding hills ex- 

 hibit each one its own vault-like dome, while all are united with 

 the central ellipsoid of the Brocken itself; and in many other coun- 

 tries the same phenomenon may be observed, not only in northern 

 Europe, but even in the southern part of India. In this latter 

 country, Mr. Newbold informs us (Asiatic Journal, May, 1842), 

 that the table land of Mysore exhibits similar spheroidal masses 

 of granite, and observes, that the well-known experiments of Mr. 

 Gregory Watt might have led us to expect such a result, as con- 

 sequent upon the cooling of the rock after its elevation. 



It thus appears that vaulted cavities, noticed in ellipsoidal 

 granite, cannot be looked upon as the result of decay, but are, like 

 the myriads of blocks described, the natural results consequent 

 upon the elevation of the whole mass of the granite and the cir- 

 cumstances under which it was forced through the surface, like a 

 bubble, from the interior of the earth. 



D. T. A. 



