Origin of Crystalline Limestone. 129 



the sphere of action of other volcanoes now active, such as 

 those of Teneriffe, Ponza Isles.* On the other hand, there 

 could not have heen complete fusion ; for in the crystalline 

 limestone of Norway, MM. Naumann and Keilhau have ob- 

 served fragments of corals. f 



The nature of the very numerous minerals of the crystalline 

 limestone also gives great improbability to the hypothesis of 

 complete fusion. It appears, indeed, that rocks which have 

 been reduced to a fluid state, and which have had an igneous 

 origin, such as lavas, have always a very simple mineralogical 

 composition. They are essentially formed of two minerals : 

 the one of the felspar class, in which are concentrated the 

 alumine and the alkalies ; the other of the pyroxene or peri- 

 dote kind, in which are concentrated the oxide of iron, mag- 

 nesia, and lime. In " crystalline" limestone, on the contrary, 

 there are various silicates, sometimes with a single base, 

 sometimes with many ; and these silicates are often associ- 

 ated either with free silex or with silicates, not saturated 

 with bases. Moreover, together with these silicates, there 

 are very energetic uncombined bases, such as magnesia 

 (periclase), alumine (corindon). There are also metallic ox- 

 ides, such as the oxides of iron, which, under certain circum- 

 stances, appear to have been contemporary with the lime- 

 stone ; and there are compound oxides, such as the spinelles, 

 perovskite, in which the oxide, playing the part of an acid 

 (alumine, titanic acid), is an acid much less energetic than 

 the silex. We easily comprehend, then, that these minerals 

 have been formed with the concurrence of heat, or of the 

 molecular actions which it developed ; but it is difficult to 

 admit that they result from a complete fusion of the crystal- 

 line limestone. 



Moreover, many facts prove that felspar may be formed 

 in rocks without the intervention of a great heat ; for exam- 

 ple, in the Arkose of La Poirie (Vosges), crystals of felspar 

 are developed in the clay lands (argilolites), which certainly 

 have not been melted, and the stratification of which is quite 



* Dufrenoy, Ann. des Mines, 3 sec, tome xi., p. 385. 

 t See also Translation of Professor Scheerer's Memoir, sujira, p. 7. — Ed. 

 VOL. LVI. NO. CXL — JANUARY 1854, I 



