128 Analysis, ^c. of Cordier''s Essay upon the 



masses in the Pampas between Buenos Ayres and Chili, may 

 be cited in addition. But what shall we say of the numer- 

 ous masses of metallic copper in the talcose district of Lake 

 Superior, which are partly described by Mr. Schoolcraft ? 

 Are they not also meteoric ? If they be, Cordier's argument 

 may prove too much. 



*' 24. If Halley's hypothesis be admissible, it suggests a limit 

 to the interior temperature of the earth. This limit is the resis- 

 tance which forged iron subjected to enormous pressure opposes 

 to fusion. We might be tempted perhaps to reduce th s tempe- 

 rature, on considering the experiments of Nevvton confirmed by 

 Barlow, which prove that iron at a white heat loses its magnetic 

 virtue. On the other hand, we must not forget that an excessive 

 compression of the metal is likely to retard the limit where the 

 magnetic virtue is thus destroyed. 



"25. In fine, in adopting this hypothesis, we shall be justified 

 in examining some very feeble effects, secular, and not hitherto 

 perceived, which the various positions and irregular figure of an 

 interior solid mass, possessing a peculiar motion, and partly com- 

 posed of metallic iron, might occasion. For instance, we should 

 be led to doubt the perfect and absolute iiivariability, which we 

 have hitherto ascribed to a plummet line in every place : this 

 doubt would extend to countries situated far from the bands or 

 zones without declination, and from the magnetic equator. 



" Such are the principal deductions to which we are led by 

 introducing the hypothesis of heat and central fluidity, in the 

 midst of questions of the highest importance to geology. It would 

 be easy to extend these inductions ; and to explam for instance in 

 a satisfactory manner the formation of primordial, unstratified 

 rocks, those of the intermediate (transition) districts, veins, gyp- 

 seous, sulphurous, saline, calcareous and magnesian strata of the 

 secondary class. The fecundity of application is remarkable ; 

 and tends to prove the probability of the theory. This would 

 not be the case with the Neptunian hypothesis, which has reign- 

 ed so long, and which represents our globe as a mass solid even 

 to the center, cold, inert, and formed throughout of aqueous de- 

 positions. 



" This system has remained barren ; and no part of it will now 

 bear an accurate examination. It is now reduced to narrow lim- 

 its, to the explanation of those superficial layers formed of con- 

 solidated sediment, conglomerated fragments, and organic re- 

 mains, which form, almost etitirely, the very thin covering which 

 is called the secondary set of formations. Had not the author- 

 ity of th'^ scientific men who brought this Neptunian system mto 

 credit produced an illusion, it would long ago have been subject- 



