256 Naumann on Primitive Formations. 



At present there are especially two hypotheses maintained by 

 different parties, regarding the origin of gneiss, and of the rocks 

 associated with it. The first of these theories is founded on the 

 •notion of the metamorphisni of rocks, and the second, on the 

 theory of the originally fused condition of our planet. • 



The great majority of the geologists of the present day in- 

 cline to the opinion that these oldest cryptogenous rocks, as wel 

 as the recent formations resembling them, have been produced 

 hj a peculiar metamorphosis of preexisting sedimentary strata » 

 consisting essentially in a recrystallisation of the materials of 

 these strata, and caused either by a high temperature, or by mole- 

 cular movements excited in some other way. 



The supporters of this theory found it especially upon the 

 parallel structure and stratification of these rocks, upon the indis- 

 putable fact that clay-slate in the neighborhood of large granite 

 masses is frequently changed into mica-schist and rocks of a 

 gneissoid character, and upon the scarcely doubtful fact that in 

 many countries, gradual transitions may be followed, from gneiss, 

 through mica-schist and clay-slate, into grey wacke slate. By these 

 transitions, gneiss is brought into such close connection with 

 grey wacke slate, that these appear only as the extreme members of 

 ^ single series ; for the whole of which one and the same original 

 mode of formation must be assumed. Now since greywacke 

 slate is undoubtedly a sedimentary rock, the clay-slate, mica-schist 

 and gneiss lying under it, must have been something similar. But 

 because the mineralogical composition and the crystalline nature 

 of these deeper rocks appear the more opposed to this inference 

 the deeper they lie, the disciples of the metamorphic theory were 

 obliged to suppose the action of a metamorphism working from 

 beneath, which has reacted upon, and so altered these oldest sedi- 

 mentary strata, that they now appear as gneiss and mica-schist. 



This theory, which at the first glance appears so satisfactory, 

 was first enunciated by Boue in 1822, was afterwards adopted by 

 many other geologists, and found in the year 1833 more decided 

 expression through Lyell,who gave the strata thus altered the name 

 of hypogenous metamorphic rocks ; a title which is intended to 

 indicate a metamorphosis which took place in the depths of the 

 earth's crust, and proceeded from beneath upwards. Properly 

 speaking, these views were very similar to those which Hutton 

 attempted to establis h in the years 1V88 and 1Y95,* and bis 



* His Theory of the Earth appeared for the first time in the Edinburgh 

 Philosophical Transactions for 1788. 



