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of gas, filled with green earth, and crystals of 

 pyroxene and mesotype. Their basis is grayish 

 blue, rather soft, and displays small white spots, 

 which, by the regular form they affect, I should con- 

 ceive to be decomposed feld-spar. Mr. von Buch 

 has examined with a powerful lens the species we 

 brought. He has discovered, that each crystal 

 of pyroxene^ envelopped in the earthy mass, is 

 separated from it by fissures parallel to the sides 

 of the crystal. These fissures seem to be the 

 effect of a contraction, which the mass or basis 

 of the mandelstein has undergone. I sometimes 

 saw these balls of mandelstein arranged in strata, 

 and separated from each other by beds of 

 grnenstein of ten or fourteen inches thick ; 

 sometimes (and this situation is the most com- 

 mon) the balls of mandelstein, two or three feet 

 in diameter, are found in heaps, and form little 

 mounts with rounded summits, like the sphe- 

 roidal basaltes. The clay, which separates these 

 amygdaloid concretions, arises from the decom- 

 position of their crust. They acquire by the 

 contact of the air a very thin coating of yellow 

 ochre. 



South- West of the village of Parapara rises 

 the little Cerro de Flores, which is distinguished 

 from afar in the steppes. Almost at it's foot, 

 and in the midst of the mandelstein tract, which 

 we have just been describing, a porphyritic 

 phonolite, a mass of compact feld-spar, of a 



