8 GEOLOGICAL SURVEY 
The absence of organic remains observed in the metamorphic rocks, could only arise from one of 
three causes; 1. That they were deposited before the appearance of either animals or vegetables 
on the earth. 2. That their deposition took place under circumstances unfavorable to the preserva- 
tion of organic remains. 3. Or, if they ever did contain such remains, every trace of them has 
been obliterated by the high temperature to which they have been subjected during their consoli- 
dation. 
Still we must not be too hasty in concluding that, because no organic remains are found, no 
organized beings existed at the time of the deposition of the rocks. Prof. Forbes has shown, in a 
report made to the British Association, on the distribution of the Mullusca and Radiata, that at a 
depth estimated at 300 fathoms, and which he calls the zero of lite, all animals cease to exist. 
The passage of the metamorphic rocks into the oldest fossiliferous strata, is so gradual, that it is 
often difficult, if not impossible, to distinguish one from the other ; so that it is probable that some, 
at least, of the metamorphic rocks did once contain organic remains, every trace of which has disap- 
peared. The chemical constitution of metamorphic limestones leads also to this conclusion. _ It is, 
however, highly probable, from the gradation apparent in the order of creation, as unfolded by the 
monuments preserved in the fossiliferous rocks, that the beginning of life, on our planet, was not 
far removed from the period of deposition of the newer metamorphic rocks. 
FoRMATIONS, SysteMs, SERIES oR PERIODS. 
Groups of strata, having some common characteristics, are often united under the term Formation, 
as “Eocene and Miocene formations.” Several formations may again be united under the more- 
comprehensive term System, as when we speak of the “ Carboniferous system,” which includes the 
coal formation, and numerous strata of lime-rock and sandstone. A still higher generalization 
includes a number of systems under the name of Period or Series—thus we have the “ Secondary 
and Tertiary Series or Periods.” 
The formations composing the metamorphic rocks have no invariable order of superposition, 
although they generally overlie each other, in the following manner: 
Clay Slate, 
Talcose Slate, 
Mica Slate, 
Hornblende Slate, 
Gneiss. 
Besides these, beds of limestone, quartz rock, chlorite slate and soapstone, form no inconsiderable 
portion of the metamorphic rocks. 
Gneiss is a-compound rock, differing from granite only in having a stratified structure. It is 
composed of quartz, feldspar, and mica. These minerals are disposed in layers, which gives the 
rock a slaty or schistose structure, and a striped appearance sometimes. These layers are 
exceedingly regular, and the rock may be split into flagging-stones: they are, however, often so 
much bent as to give the massa singularly contorted appearance. Gneiss frequently loses its slaty 
structure, and then it can scarcely be distinguished from granite; and hence the name greissoid 
granite. ‘Table Rock, in Pickens District, is a magnificent example of the occurrence of gneiss i 
beds of vast thickness. 
