242 Miller on the Taconic 
shown that the Potsdam sandstone rests directly upon the 
Swanton or Black Slate group as originally asserted by Em- 
mons, and that both the Swanton group and the Georgia group 
are fossiliferous. 
The Taconic rocks extend from Canada East and Maine to 
Georgia and Alabama, flanking almost continuously the ranges 
of mountains upon both the eastern and western slopes. Their 
thickness in New Hampshire is over four miles, and in Ver- 
mont the maximum must exceed five miles. The slate belts of 
York and Lancaster counties. Pa., and the rocks containing 
the valuable ores of nickel and copper, belong to this system. 
There are five extensive outcrops in North Carolina, and three 
or four subordinate ones. They rest unconformably upon the 
belts of the exposed Laurentian, and very much resemble, in 
their characters, the subdivisions in Vermont and New York. 
The largest outcrop is from 20 to 40 miles wide, and extends 
quite across the state. The maximum thickness exceeds five 
miles. There are large outcrops in Virginia, South Carolina, 
Georgia and Tennessee, and limited outcrops in Alabama. Gold, 
silver, copper, lead, iron and other valuable minerals occur in 
these rocks, not only in veins, fissures, and dykes, but in seams 
following stratification, and as parts of the sedimentary materi- 
als. In northern Georgia gold exists in seams with milky 
quartz, following the stratification of hornblende schists, and 
constituting as truly sedimentary rocks as the schists themselves 
do. The seams are stratified within the slaty sediments, and 
are of the same age as the Taconic system. These seams are 
so constant that they characterize the slates and schists, in the 
Appalachian system. They are metalliferous, and frequently 
auriferous or cupriferous. The magnetic, and specular iron 
ores also occur, with the material of the slates, as a deposit of 
the same age, and constituting part of the same system. This 
mineral wealth is so distributed that it is practically inexhaust- 
ible. The Taconic appears in Missouri, Arkansas and Texas. 
The iron ore districts, about Iron mountain and Pilot Knob, con- 
taining porphyry rocks, is of this age, but the granite to the east is 
Laurentian. The ore is found in very thick veins, in Iron and 
Shepard mountains and Pilot Knob. It is specular ore con- 
taining betweet 60 and 75 per cent of iron, free from sulphur 
