chap. xiv. Gypseous Formation. 509 



20th. Many thin strata of compact, fine-grained, 

 pale purple sandstone. 



21st. Gypsum in a nearly pure state, about 300 feet 

 in thickness : this bed, in its concretions of anhydrite 

 and layers of small blackish crystals of carbonate of 

 lime, exactly resembles the great gypseous beds in the 

 Peuquenes range. 



22nd. Pale purple and reddish sandstone, as in bed 

 20 : about 300 feet in thickness. 



23rd. A thick mass composed of layers, often as 

 thin as paper and convoluted, of pure gypsum with 

 others very impure, of a purplish colour. 



24th. Pure gypsum, thick mass. 



25th. Red sandstones, of great thickness. 



26th. Pure gypsum, of great thickness. 



27th. Alternating layers of pure and impure gypsum, 

 of great thickness. 



I was not able to ascend to these few last great 

 strata, which compose the neighbouring loftiest pin- 

 nacles. The thickness, from the lowest to the uppermost 

 bed of gypsum, cannot be less than 2,000 feet : the beds 

 beneath I estimated at 3,000 feet, and this does not 

 include either the lower parts of the porphyritic conglo- 

 merate, or the altered clay-slate ; I conceive the total 

 thickness must be about 6,000 feet. I distinctly 

 observed that not only the gypsum, but the alternating 

 sandstones and conglomerates were lens-shaped, and 

 repeatedly thinned out and replaced each other : thus 

 in the distance of about a mile, a bed 300 feet thick of 

 sandstone between two beds of gypsum, thinned out to 

 nothing and disappeared. The lower part of this section 

 diners remarkably, — in the much greater diversity of 

 its mineralogical composition, — in the abundance of 

 calcareous matter, — in the greater coarseness of some 

 of the conglomerates, — and in the numerous particles 



