ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 463 



stratification of sedimentary strata. The stratification of gneiss 

 and gneissoid rocks has not unfrequently been denied. Thus 

 Featherstonhaugh declared, that "what has been called the stratifi- 

 cation of these igneous rocks, may be owing to the principle which 

 occasions their fissility." Coquand regards gneiss as a "granite 

 strato'ide, mais non stratifie."* Riviere opines also that gneiss 

 does not form true layers, but is only a fissile or pseudo-stratified 

 rock.f Even McCulloch makes the following admission: 

 ■" Gneiss has not yet indeed presented any decided marks of that 

 mechanical arrangement which so often occurs in the other 

 stratified rocks ; since I must explain the parallelism of the mica 

 which has been supposed a proof of such arrangements, in a very 

 different way. In hypers thene rock, an unstratified member of 

 the trap family, the crystals of that mineral often occur in a 

 similar laminar manner, so as to communicate a fissile tendency 

 to it ; and in Kerrara mica itself is thus found not only in a 

 mass of trap, but in a vein of the same substance, with the 

 same parallelism to the sides of the vein as it has to the plane cf 

 the stratum in micaceous schist." J The idea that gneiss may 

 have been formed in the manner above indicated is not entirely 

 new. In 1845 it was stated that the gneiss of the Saxon Erzge- 

 birge " perhaps differs only from granite because it solidified 

 under the influence of certain pressures or tensions.[| 



Whether the explanation here attempted of the parallel struc- 

 ture of gneiss may be regarded as .adequate or not, it does not at 

 anv rate seem to be any more far-fetched than the theory which 

 attributes this phenomenon to the influence of electrio magnetic 

 currents (Scheerer's theory) or even than that which regards gneiss 

 as a sedimentary rock, altered in some obscure manner by heat 

 or other agencies. Besides the arguments given above ^in support 

 of the first mentioned view, there are also some general considera- 

 tions in favor of the existence of a primitive formation, which are 

 stated as follows by Naumann.§ "The oldest sedimentary forma- 

 tions must have had some material from which they could be 

 formed, and a foundation on which to be deposited. The whole 

 .•series of sedimentary formations must have been borne by some- 

 thing, and the material of at least the first member of this series 



* Bull, de la Soc. Geol. tome ix. 1838, p. 222. 

 f Compte rendus, tome xxv. 1847, p. 898. 

 t System of Geology, Vol. II. p. 152. 



|| Geognostische Beschreibung des Eonigreicb.es Sachsen, 2tesHeft, p. 

 122. , 



§ Lebrbucb der Geognosie, ii., p. 8. 



