82 On the Erratic Formation of North America. 



This gives the empirical formula, 3Ni + C + 6H = NiC 

 + 2Ni 6 H, or Ni C + 2 (Ni Ha), 



When we remember the isomorphism of magnesia and 

 oxide of nickel, it will be agreed by all who attach any value 

 to this agency in modifying minerals, that we may have many 

 cases in which these two oxides are mutually interchanged. 

 Hence we find, at the Texas locality, dolomitic carbonates 

 with a faint tint of green, derived from a small trace of oxide 

 of nickel present in them ; others of green colour several 

 shades deeper ; and others which closely approach the high 

 colour and other properties of the pure hydrous carbonate of 

 nickel described in this paper. In some specimens, unques- 

 tionable emerald nickel is found mechanically mingled with 

 and coating whitish dolomite. I cannot agree with the 

 opinion expressed by Professor Shepard, at page 250 of this 

 volume, that these varieties are distinct species. Certainly 

 we must demand analysis to shew that the Mg and Ni 

 are in fixed atomic proportions with water, before the " hy- 

 drated carbonate of magnesia and nickel'' can be regarded 

 as a true species. — [The American Journal of Science and 

 Arts, Second Series, vol. vi., No. 17, p. 248.) 



On the Erratic Formation of North America. Letter from 

 M. Desor to M. DE Verneuil, dated Boston, November 

 7, 1847. 



This letter of M. Desor appears to us destined to have a great in- 

 fluence on the numerous discussions undertaken, with a view to fix 

 the origin of the erratic phenomenon of the north. Indeed, it fur- 

 nishes us with a new and capital fact, namely, the association of 

 marine shells with the polished and striated pebbles of the true drift. 

 This fact was completely unknown till the moment when MM. Desor 

 and De Pourtalis discovered it. The following is an extract from the 

 letter ; — 



The erratic formation of America is composed of two stages, the 

 drift, amorphous and without stratification in the lower part, and the 



