FOREIGN COKRESPONDEN'CK. 
247 
cai-boii, and uon-cry;jtalliiie. Tlio aul|iliui- of the first category is that 
extracted from eomhinalions iu which sulphur enters as the ek^ctro- 
ueoativc eh'uieiit, as iu sul2:)hurette(l liydrogen and tlie different 
metallic sul|)hides. That of the second categovy is extracted from 
combinatious iu which it forms, on the contrary, the electro-positive 
element, as in sulphureous acid, sulphuric acid, and their salts, &c. 
The sulphur we received from Sicily is in large transparent ciystals 
lielonging to the third crystalline system, having for type the prism 
witii a rectangular basis, or, as the French crystal lographers term it, 
/(' si/.<tihne pri^nudiijiK; vertaiujnlaire drotf. It therefoi'e is identical 
with M. Eerthelot's octahedral or electro -negative sulphur; and, to 
assure myself of this, I treated it with srdphido of carbon, and found 
that it was completely soluble in this liquid, leavmg not the slightest 
I'esiduuni. These natural crystals are, moreover, very beautifvd, being 
of a transparent yellow colour, and showing, here and there, in their 
superficies or in their interior, the colours of the rainbow. 
It appears evident enough, from what wo have just stated, 1st, that 
this Sicilian sulphur has been crystallized in nature from a solution 
and not by fusion — for sulphur, when crystallized by fusion, takes the 
form of long prismatic needles belonging to another (the 5th) crys- 
talline system {ai/steme prismat'iquc ohlirpie) ; its origin cannot, there- 
fore, be immediately attributed to volcanic eruption. 2ndly, that if 
this sulphiu" be owing to the decomposition of any soluble combinations 
in which this element enters, it must evidently have come from sucli 
as contain it as an electro-negative element. For instance, from 
sulphuretted hydrogen, or certain metallic sulphides, and not from 
sulph\irous acid, from sidphnric acid, or their salts. 
M. Lesfjnerenx has read liefore the Soriefc de N<'iifcJiatd a paper 
on the formation of prairies in America, which concerns at once 
botanical geography and geology. The problem which tlie author 
has just endeavoured to solve, namely, the cause of the formation of 
these vast American prairies, is as interesting to the geologist as to 
the botanist, and, on this account, we will expose here the facts con- 
tained in Lesf]noren\'s memoir, which wc consider most worthy of 
iiotice. 
In nature, for<;sts and [irairiesarc not often met with simultaneously 
or intermingled one with the other, even on large portions of territory ; 
on the contrary, they are seen to stretch srpfindi'hj over vast tracts of 
