373 French National InJlUute. 



have tonfidered as tlie ibis, but another fpecies which h< 

 defcribes. 



The third memoir is by Hatiy on a variety of martial 

 pyrites, or fulpiiat of iron, to wliicli the autlior gives tlie 

 name of tnacontocJra, becaufe its crvftals have thirty faces, 

 ■fix of which are rhombs and twenty-four trapezoids. JbJaiiy 

 has explained the laws of drecrement fruni which thefe 

 tryflals refult, and demonftrate fome curious properties of 

 this foHd, to which geometricians hitherto have paid httlc 

 attention. 



Tlie ilruclurc of the earth, and the rcfpc(!:livc pofition 

 of the materials of wliich it is compofed, are among thofe 

 curious points of natural hiflory (till involved in confider- 

 able obfcurity. We can ftudy only the outer cruft of the 

 globe, and even this cruR is attended with manv difficulties. 

 Happily for our curiofity, the nucleus in the high chains 

 of mountains i'eems, by fwelling up, to have burll tlie 

 matter by which it is enveloped, and to have fliown itfelf 

 uncovered. The labours of a Sauflure, a Delue, a Palla.-, 

 and a Dolomieu, have confirmed that the greater part oi 

 the large chains are compofed of fmall parallel chains, of 

 which that in the middle, commonly the higlicft, confills of 

 granite, the two collateral ones confift of I'chift and Hones 

 of an analogous kind, and the outer ones of calcareous fub- 

 ftanccs. Tbis general rule, which throws the greateft lisiht 

 on the theory of the earth, did not feem to be applicable 

 to the Pvrcnnees ; there every thing feemed to be without 

 order. The highcft fummits of Alount Perdu and Ic Mar- 

 bore are certainly calcareous, and, as fume alTcrt, contain 

 petrified Ihells. C. Ramond, by laborious journeys and in- 

 genious dedu(!rtions, has difcovered the fource of this embar- 

 rafl'uient. It anfcs from the fmall chains being in ait 

 obliqui direction, and from the fchiftous and calcareous 

 bauds fituated towards Spain, being not only higher than 

 thofe of the fame nature towards France, but furpaffing 

 even the granitic hand, which forms the axis of the chain ; 

 fo that the ridge which determines the fall of the ftreams is 

 different from the geological ridge. 



The clafs in its lalt fittings has been occupied witli two. 



objeds 



