Natural' Historical Collections. 295 



Xestrial species. Besides these animals with aerial respiration and cold blood, 

 one genus of terrestrial mammalia and many insects, are the only beings of this 

 period which had need of dry land. The third period, connected in some degree 

 with the present epoch, abounds in organic remains ; the terrestrial mammifera, 

 with the mollusca and the insects, which live on the surface of the land are more 

 numerous, compared with the species which have lived in the waters, as their re- 

 mains are found in the more recent strata. In inferior numbers in the mid- 

 dle fonnation of the tertiary series, where they only begin to appear, the terres- 

 trial mammifera afterwards predominated over the marine species of the same 

 class, and at last ahnost exclusively composed the population which perished at 

 the time of the dispersion of the ^uvial formations which cover and terminate 

 the series of tertiary deposits. 



Analysis of Phonolitic Rocks M. Gmelin divides volcanic rocks into two 



classes, the basaltic and the trachytic, between which the phonolitic rocks are in- 

 termediate. The phonolites are composed of feldspar and a zeolitic substance, 

 which is most commonly mesotype. These two minerals may easily be separated 

 from each other, by treating the rock, reduced to an impalpable powder, with mu- 

 riatic acid of medium strength for twenty-four hours. The zeolite is decomposed, 

 and the feldspar is unchanged. We separate from the latter the silica with 

 which it is mixed, by boiling it in a solution of carbonate of potass, and the ana- 

 lysis of the residue may then be made by dissolving it with carbonate of baryta. 



By this process M. Gmelin has arrived at the following results : 



1. Phonolite of Hohenkr'dken, in the Hegau ; of a clear brownish gray, spe- 

 cific gravity 2.504. The zeolitic portion contains in 100 parts, silex 43.44 ; 

 alum 22.89 ; soda 13.67 ; potass 5.45 ; lime 2.44 ; protoxide of iron 2.66 ; oxide 

 ef manganese 1.19; sulphuric acid 0.22; water 5.77. The feldspathic part is 

 composed of silex 66.55 ; alum 15.86 ; soda and potass 9.44 ; lime 1.27 ; pro- 

 toxide of iron 4.63 ; oxide of manganese 0.98. The specimen analyzed con- 

 tains 55 parts of zeolite. 



2. Phonolite of Pferdekuppe, in the Rhongebirge ; of a greenish-gray, de- 

 composed at the surface, sp. gr. 2.605. This analysis accords in a remarkable 

 oianner with that of the phonolite of Hegau. It gives 13.7 of zeolite. 



3. Phonolite of Abstrode, in the Rhongebirge ; similar to the preceding, and 

 decomposed at the surface to the depth of three lines. The unaltered part con- 

 tains 15.8 of zeolite ; the altered portion contains 0.42 of matter soluble in acids. 



The preceding analyses show, in the most decisive manner, that the phonolites 

 of Hegau and of Rhongebirge are mixtures of feldspar and mesotype. The for- 

 mer predominates in the rocks of Rhongebirge ; those of Hegau, on the other 

 hand, contain a greater proportion of mesotype. The part upon which acids 

 act, approaches in its composition sometimes to natrolite, at others to mesolite 

 or mesoline ; but it always contains a less proportion of water. The composition 

 of the other portion agrees precisely with that of feldspar, and may be represented 

 by the formula, 



21 S3 -f 3AS3. 



The phonolites contain a greater quantity of zeolite in proportion as they are 

 lighter, and as they contain more alum. When the rocks are clianged by the 

 action of the air, they are transformed into almost pure feldspar, and the zeolitic 

 portion is decomposed. We may say that the phonolites are characterized by the 

 abundance of potass and soda, as the basalts are by the great proportion of prot- 

 oxide of iron and of magnesia which they contain. 



The phonolitic formations are known to be extremely fertile, and particularly 

 adapted to the cultivation of the vine. It is probable that this may arise from 

 these rocks imparting to the soil a great quantity of alkali during decomposition. 

 — Naturwissench. Abhandlungen, Vol. II. p. 133. 



