26 GEOLOGICAL MEMOIRS. 



nated Metamorphic, The term Plutonian comprises those rocks 

 which have heen produced hy igneous action from internal causes, and 

 have been therefore called by Humboldt endogenes. Such rocks are 

 crystalline and sometimes cellular, are felspathic, and appear either 

 in masses or have been erupted, hke lavas, in streams. 



By the term " Geyserian " M. Dumont proposes to designate 

 those rocks which, though, like the Plutonian, they have been pro- 

 duced by causes acting from within, have not, Uke them, been fused 

 by heat, but have been formed by either aqueous or gaseous emana- 

 tions. The Plutonian, in fact, have been formed like lavas, the Gey. 

 serian like sublimed sulphur. Geyserian rocks are metalliferous, 

 rarely felspathic, are confusedly crystalline, concretionary or cellular, 

 and exhibit a very different aspect to that of the Plutonian. On the 

 other hand, though sometimes conglomeratic or composed of trans- 

 ported materials, and formed under the influence of water, they are 

 distinguished from the Neptunian by their want of stratification, by 

 the metallic and mineral substances they contain, by the absence of 

 organic remains, by a crystalline or concretionary structure, and 

 especially by their mode of formation. 



Such are the views of M. Dumont ; and although, as he states, it 

 may be sometimes difiicult to draw the line of limitation between rocks 

 of these various modes of formation, and the Geyserian may appear 

 involved in and subsidiary, sometimes to the Plutonian, sometimes 

 to the Neptunian, it is certainly desirable that the geologist should 

 feel and admit that igneous fusion alone, as supposed to be recog- 

 nized in plutonic rocks, or the ordinary action, whether mechanical or 

 chemical, of water, as recognized in Neptvmian rocks, cannot explain 

 all the phsenomena of rock-formations and of mineral veins ; whilst 

 the term "Geyserian" sufficiently explains the nature of the other 

 actions M. Dumont considers to have shared in the production of the 

 general effects observed. 



[J. E. P.] 



On Titanium in the Harz. By Fr. Ulrich. 



[Leonhard u. Bronn's N. Jahrb. f. Min. u. s. w. 1853, p. 175 : Bericht d. Verhandl. 

 d. Clausthaler Vereins. 1852, p. 29 et seq.'] 



Zimmerman has mentioned the occurrence in the Harz of Rutile 

 and Nigrine, which have been found in the Baste and as rolled frag- 

 ments on the Ecker. Titanite has now also been met with. A 

 short distance above the uppermost quarry of the Radau Thai there 

 is a vein traversing a kind of mica-schist. The vein is 3 feet thick, 

 and is chiefly occupied by crystalline, coarse-grained Orthoclase, 

 columns of which, from ^ to 1 inch long, are intermingled with a 

 mineral decomposing into yellow and brown hydrated oxide of iron. 

 The Titanite is found throughout the mass of the felspar in little 

 particles and in crystals, of a clear and honey-yellow colour, and 

 about 2 inches in length. The vein also bears quartz and a thick 

 greyish white mineral, which perhaps may be Wernerite ; in that case, 

 according to Wohler, Apatite also, 



[T. R. J.] 



