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^, 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 ishor. 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 ; 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. 



+ Ur-gruenstein. I remember having seen similar balls 

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

 stein, in the margraviat of Bayreuth. I sent several balls 

 from Antimano to the collection of the king of Spain at 

 Madrid. See the description of the geological specimens 

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

 Hist. Naiy vol ii, p. 282—271.) 



