60 



perpendicular, cut all the mica-slate strata % 

 and are nearly from six to eight toises thick. 

 These veins contain, not fragments, but balls or 

 spheres of granular diabasis-j-, formed of con- 

 centric layers. These balls are composed of 

 lamellar feldspar and hornblende intimately 

 mixed together. The feldspar approaches some- 

 times to vitreous feldspar, when it is dissemi- 

 nated in very thin laminae in a mass of granular 

 diabasis, decomposed, and emitting a strong 

 argillaceous smell. The diameter of the spheres 

 is very unequal, sometimes four or eight inches, 

 sometimes three or four feet ; their nucleus is 

 more dense, without concentric layers, and of a 

 bottle-green, inclining to black. I could not 

 perceive any mica in them ; but, what is very 

 remarkable, great quantities of disseminated 



* The direction of the mica-slate is hor. 12*2 ; dip. 72° 

 East. Veins of gneiss, and even of granite, of new forma- 

 tion, are very common in the metalliferous mountains (Erz- 

 gebirge) of Saxony j which, as we have already remarked, 

 bear much analogy to the environs of Caraccas. There are 

 veins of granite in the gneiss at Geyer, and in the mica-slate 

 of Johanngeorgenstadt. 



f Ur-gruenstein. I remember having seen similar balls 

 filling a vein in transition-slate, near the castle of Schauen- 

 stein in the margraviat of Bayreutb. I sent several balls 

 from Antimano to the collection of the king of Spain at Ma- 

 drid. See the description of the geological specimens from 

 Caraccas, in my letter to Don Joseph Clavijo. (Ann. de Hist, 

 Nat., vol. ii, p. 262—271.) 



