IEST DISCOVERY OF THE ALTTM. 117 



formation lying on the primitive mica-slate of Araya, or 

 whether it owe its origin merely to a change of composition 

 and texture in the beds of mica-slate. I lean to the latter 

 proposition ; for the transition is progressive, and the clay- 

 slate (thonschiefer) and mica-slate appear to me to con- 

 stitute here but one formation. The presence of cyanite, 

 rutile-titanite, and garnets, and the absence of Lydian 

 stone, and all fragmentary or arenaceous rocks, seem to 

 characterise the tormation we describe as primitive. It is 

 asserted, that even in Europe ampelite and green stone are 

 found, though rarely, in slates anterior to transition-slate. 



When, in 1785, after an earthquake, a great rocky mass 

 was broken off in the Aroyo del Robalo, the Guaykeries of 

 Los Serritos collected fragments of alum five or six inches 

 in diameter, extremely pure and transparent. It was sold 

 in my time at Cumana to the dyers and tanners, at the 

 price ol two reals* per pound, while alum from Spain cost 

 twelve reals. This difference of price was more the result 

 of prejudice, and of the impediments to trade, than of the 

 inferior quality of the alum of the country, which is fit for 

 use without undergoing any purification. It is also found 

 in the chain of mica-slate and clay-slate, on the north-west 

 coast of the island of Trinidad, at Margareta, and near Cape 

 rhupariiparu, north of the Cerro del Distiladero.f The 

 Indians, who are naturally addicted to concealment, are 

 not inclined to make known the spots whence they obtain 

 native alum ; but it must be abundant, for I have seen very 

 considerable quantities of it in their possession at a time. 



South America at present receives its alum from Europe, 

 as Europe in its turn received it from the natives of Asia 

 previous to the fifteenth century. Mineralogists, before my 

 travels, knew no substances which, without addition, calcined 

 or not calcined, could directly yield alum (sulphate of 

 alumina and potash), except rocks of trachytic formation, 



* The real is about 6i<f. English. 



t Another place was mentioned to us, west of Bordones, the Puerto 

 Escondido. But that coast appeared to me to he wholly calcareous ; and 

 I cannot conceive where could be the situation of ampelite and native 

 alum on this point. Was it in the beds of slaty clay that alternate with 

 the alpine limestone of Cumanacoa ? Fibrous alum is found in Europe 

 only in formations posterior to those of transition, in lignites, and other 

 tertiary formations belonging to the lignites. 



