102 



ing rocks lined with capillary sulphat of alumin 

 in effervescence ; and real beds, two inches thick, 

 full of native alum, stretched as far as the eye 

 could reach in the clayslate. The alum is gray- 

 ish white, somewhat dull at the exterior, and of 

 an almost glassy lustre within. It's fracture is 

 not fibrous, but imperfectly conchoid. It is 

 hemidiaphanous, when it's fragments are thin ; 

 and has a sweetish and astringent taste, without 

 any bitter mixture. I proposed to myself the 

 question even on the spot, whether this alum, 

 so pure, and filling beds in the clayslate without 

 leaving the smallest void, be of a contemporary 

 formation with the rock ; or must be admitted 

 to be of a recent, and in some sort secondary 

 origin, like the muriat of soda, found sometimes 

 in small veins, where strongly concentrated 

 springs traverse beds of gypsum or clay. No- 

 thing in these places seems to indicate a mode 

 of formation, which may be renewed in our days. 

 The slaty rock exhibits no open cleft ; and par- 

 ticularly none is found parallel to the direction 

 of the slates. It may also be inquired, whether 

 this aluminous slate be a transition formation 

 lying on the primitive micaslate of Araya, or 

 arise merely from a change of composition and 

 texture in the beds of micaslate. I lean toward 

 the latter proposition ; for the transition is pro- 

 gressive, and the argillaceous slate (thonschiefer) 

 and micaslate appear to me to constitute here 



