TIES! DISCOVElil' OE TilE AHril. 
117 
formation lying on the primitive mica-slate of Araya, or 
**'hether it owe its origin merely to a change of composition 
*nd texture in the beds of mica-slate. I lean to the latter 
proposition ; for the transition is progressive, and the elay- 
siate (thonschiefer) and mica-slate appear to me to con- 
stitute here but one formation. The presence of cyanite, 
* iitile-titanite, and garnets, and the absence of Lydian 
fragmentary or arenaceous rocks, seem to 
•Characterise the formation we describe as primitive. It is 
asserted, that even in Europe ampelite and green stone are 
oiind, though rarely, in slates anterior to transition-slate. 
When, in 1785, after an earthquake, a gre.at rocky mass 
''as broken off in the Aroyo del liobalo, the Guaykeries of 
• Serritos collected fragments of alum five or six inches 
diameter, extremely pure and transparent. It was sold 
’ll my time at Curaana to the dyers and tanners, at the 
price ot two reals* per pound, wliile alum from Spain cost 
'reive reals. This difference of price was more the result 
fP’!®j’i'iice, and of the impediments to trade, than of the 
’’lerior quality of the alum of the country, which is fit for 
I "’^tont undergoing any purification. It is also found 
the chain of mica-slatc and clay-slate, on the north-west 
•Oast of tiio island of Ti’inidad, at Margareta, and near Capo 
I ’upariiparu, north of the Cerro del Distiladero.f The 
'idians, who are naturally addicted to concealment, are 
’’’dined to make known the spots whence they obtain 
’re alum ; but it must be abundant, for I have seen very 
°ttsiderable quantities of it in their possession at a time. 
^iith America at present receives its alum from Europe, 
■ *1 Europe in its turn received it from the natives of Asia 
‘’.^doiis to the fifteenth century. Mineralogists, before my 
j ’"'ds,knew no substances which, without addition, calcined 
calcined, could directly yield alum (sulphate of 
’itnuia and potash), except rock's of trachytic formation, 
1 pie real is about Gl(l. English. 
place was mentioned to us, west of Bordones, the Fuertn 
I l^utthat coast appeared to me to be wholly calcareous ; and 
^ottceive where could be the situation of ampelite and native 
the in the beds of slaty clay that alternate with 
Only • ^ limestone of Cumanacoa ? Fibrous alum is found in Europe 
i^fmations posterior to those of transition, in lignites, and other 
formations belonging to the lignites. 
