The Geology of the Tallulah Gorge. — Jones. 71 
Megascopically the schist is a gray, medium grained, com- 
pact rock and exceedingly hard under the hammer. The 
schistose structure is not conspicuous in unaltered specimens, 
but shows plainly wherever weathering has taken place. Ir- 
regularly distributed masses of pyrite are quite abundant and 
on all exposed surfaces the iron oxide stain resulting from 
, their decomposition is characteristic. 
Under the microscope the rock is seen to be composed 
principally of quartz ; this material probably amounting to 
90"^ of the whole. Feldspars are next in abundance, muscovite 
probably next, pyrite, some biotite, occasional grains of mag- 
netite, small crystals of apatite and a few isolated masses of 
some irregularly shaped, highly refractive substance show- 
ing low double refraction and giving no very satisfactory in- 
dications as to its nature. 
The quartzes are in the form of irregularly shaped grains 
closely interlocked, many showing wavy extinction and all 
more or less shattered, with the cracks filled with subse- 
quently deposited silica. Nothing in the nature of a zonal 
structure or anything indicating original sedimentary mate- 
rial is to be found, but owing to the evident crushing and 
metamorphism that has taken place this can only be regarded 
as negative evidence with reference to such a possible origin. 
Of the feldspars, microline and plagioclase are the most 
abundant with some perthitic intergrowths of orthoclase and 
plagioclase. Much of the feldspar is broken and cracked like 
the quartz, but not to so great an extent. 
Some of the muscovite has undergone alteration and is ac- 
companied by granular epidote. 
The biotite is frequently accompanied by sheaf-like masses 
of minute needle-like crystals showing very high interference 
colors — doubtless rutile. A chemical determination of the 
amount of silica present would enable the rock to be classified 
with greater certainty. 
At several points along the gorge thin seams or lenticular 
masses of intercalated, highly graphitic margarite schist 
carrying crystals of tourmaline are noticeable. 
The limestone and biotite schist may have possibly had 
some influence in determining former drainage, but present 
no special features for present consideration. 
