GNEISS, MICA SCHIST, AND SLATE SYSTEMS. 657 



CHAPTER HI. 



GNEISS, MICA SCHIST, AND CLAY SLATE SYSTEMS. 



T is an opinion sustained by the force of geo- 

 logical evidence, that a time has been, in the 

 history of the earth, when it was in an in- 

 candescent condition a molten mass of 

 matter ; but whether this was its first estate 

 the commencement of that cycle of change 

 it has undergone or merely another change 

 from anterior solidity, is a point upon which 

 geology can pronounce no verdict. The 

 proof of the first hypothesis appears in the 

 universal diffusion and igneous character of 

 the granitic rocks, which, as we have had 

 occasion to remark, while constituting some 

 of the loftiest eminences of the globe, we 

 are warranted in regarding as a vast crys- 

 talline floor, upon which all the stratified 

 formations repose. The reader will bear in 



mind the fact, that at various eras subsequent to the first deposition of strata, the 

 granite pavement has undergone fusion, and been protruded in a fluid state among the 

 sedimentary formations. The production of a solid crust would be the result of this 

 incandescent igneous mass losing its heat by radiation into surrounding space, and 

 this crust would exhibit a surface diversified with inequalities, marked with projections 

 and depressions, which may be called mountains, valleys, rents, and ravines, according 

 as the various parts of the surface might radiate heat in an unequal manner. A strictly 

 analogous case is the cooling down of a mass of metal after fusion in a furnace, upon 

 which blisters and scoriae are formed, presenting a similar proportion to the quantity of 

 metal, as our highest mountains at present do to the mass of the planet. Upon the 

 ordinary atmospheric and aqueous agencies, the decomposing energy of the air, 

 the fall and percolation of rains, and the flow of streams coming into play on a solid 

 rind thus diversified a consequent disintegration must have taken place, and the 

 carrying atvay of the abraded material held in suspension or solution by the rivers, with 

 its ultimate deposition at the bottom of those basins into which they discharged their 

 waters, would be the result. In this manner we have strong grounds to believe that the 

 first stratified rocks were produced the gneiss and mica-schist systems as well as all 

 subsequent deposits ; for it is in harmony with operations that are clearly traceable as in 

 progress in the existing constitution of the earth. 



The gneiss and mica- schist with part of the slate systems form the primary strata 

 of the improved Wernerian classification ; the inferior order of Mr. Conybeare ; the 

 inferior stratified, non-fossiliferous group of Mr. De la Beche ; the metamorphic rocks of 

 Mr, Lyell ; and the Agalysian rocks of Alexander Brongniart. 



Gneiss System. The essential ingredients of gneiss are the same as granite quartz, 

 felspar and mica, or hornblende but sometimes one or more of these minerals are 



absent, and other substances supply their place, which contributes to vary the general 



u u 



