Chemical Society. 339 



at least one-third of which are unknown as British — a want of agree- 

 ment, Mr. Lyell observes, which may be partly ascribed to an im- 

 perfect knowledge of the Silurian Fauna of both countries, and 

 partly to the laws which influence the geographical distribution of 

 existing animals. The author does not deny, that, when the more 

 ancient rocks were formed, the marine species may not have enjoyed 

 a wider geographical range than now ; for when coral reefs existed 

 between the 50th and 70th degrees of latitude, a more uniform tem- 

 perature must have prevailed than at the present day ; but he con- 

 tends that there are no data for imagining that the same species were 

 ever universally distributed. 



A description of the igneous rocks of the fiord of Christiania is 

 not within the object of this communication ; but Mr. Lyell states, 

 that the island of Langoen is traversed in an east and west direction 

 by several dikes of greenstone, from two to three feet thick, but with- 

 out dislocating the strata ; he likewise mentions, that the junction of 

 the quartzose sandstone of Holmstrand with a vertical dike of felspar 

 porph)'ry thirty feet thick, is finely exhibited at Smorsteen. The 

 same porphyry also overlies the sandstone at Engnaes. The trap of 

 this district passes into a reddish granite, and the contact of the latter 

 with horizontal, thin beds of Silurian limestone and shale is exposed 

 to the height of fifteen feet at Sotfjeld, N.E. from Holmstrand ; and 

 the contact is visible on the opposite side of the fiord. At the line 

 of junction the limestone is white, and the shale is converted into 

 Lydian stone. No veins of granite penetrate the fossiliferous strata 

 in that neighbourhood, as at some places near Christiania ; and the 

 occurrence of a breccia at one point, where the limestone joins the 

 plutonic rock, induced Mr. Lyell to suspect that the latter had been 

 there protruded in a solid form. 



CHEMICAL SOCIETY OF LONDON. 



Nov. 2, 1841. — The following communications were read: 



An extract of a letter from M. Dumas " On the Analysis of 

 Atmospheric Air." 



The method of analysis adopted in these experiments was to 

 cause the air under examination to pass through the combustion 

 tube employed in organic analysis, charged with reduced metallic 

 copper, into an exhausted flask, and then weighing the resulting 

 oxide of copper and the nitrogen in the flask. M. Dumas says, " You 

 may be assured that no combination of nitrogen with copper is formed 

 in the circumstances under which we operate, a decided red heat 

 being used ; besides, all our analyses agree, as you will be able to 

 judge by the following numbers : — 



By weight. 



"April 27th, 1841, 2292 oxygen in 10,000 of atmospheric air. 

 28 2309 



during heavy rain. 



during rain,at 1 p.m. 



12 P.M., clear. 



12 A.M., cloudy. 



