24 GOLD AND TIN DEPOSITS OF SOUTHEKN APPALACHIANS. 
pinkish by the oxidation of the iron which they contain. Along the joint planes thin films 
of limonite have been deposited. 
The appearance of the rock at once suggests that it is a tuff. No conclusive evidence has 
been found to prove this assumption. Porphyritic crystals have not been observed and the 
microscope shows only very minute grains of quartz and of some other mineral much 
obscured by limonite stain. The fact that fossils have never been found in these rocks is a 
negative evidence in favor of their being volcanic tuffs. 
In places along the eastern part of the territory traversed are areas covered with a clean, 
loose quartz sand. This is the country of the " long-leaf" or turpentine pine. This deposit 
is in most places known to be thin, resting on the Piedmont rocks, and is doubtless a part 
of the Coastal Plain formations. It is regarded by Doctor Sloan as probably of Quaternary 
age. 
• CLAY. 
Comparatively small bodies of clay, like that near Grover, N C, occur in isolated locali- 
ties. They probably represent deposits, in small basins, of material derived from the decay 
of the other rocks. 
ALLUVIUM. 
Along some of the streams small flood plains have been formed. They are built up of the 
detrital material which the streams have been forced to deposit and consist principally of 
sand and gravel. These plains are. of course, the most favorable localities in which to 
search for placer deposits of valuable heavy minerals, such as gold, monazite, eassiterite, etc. 
EFFECTS OF METAMORPHISM. 
REGIONAL METAMORPIIISM. 
As may be gathered from a statement of the relative extent of the three great classes 
of rocks, this is a region characterized by the presence of metamorphic rocks. The prin- 
cipal effects of the agencies which caused the changes from their original to their present 
form have been described in the section dealing with the metamorphic rocks (pp. 14-19). 
In structure the changes have been from the stratified sediments, bedded full's, and 
massive igneous rocks to the wholly crystalline and generally much foliated schists. It 
appears probable that these mechanical changes have not been accompanied by marked 
changes i:i chemical composition; but in some cases, as that of* the qtiartzites, there has 
been pronounced silicification, while in the amphibolites some lime has doubtless been 
removed. The molecular or mineralogical changes, however, have been great. Feld- 
spars have been changed to sericite or to epidote, zoisite, calcite, and a less calcic feldspar. 
Pyroxene has been changed to amphibole. Impure kaolin has become sericite and bio- 
tit e. Garnet is a common product in many of the rocks. 
CONTACT METAMORPHISM. 
The changes induced in the surrounding rocks by the intrusion of igneous masses are of 
much less extent in this portion of the Carolinas than those produced by dynamic forces. 
Nevertheless the heat, pressure, solutions, and vapors caused by or accompanying the 
molten material have in this region had a very noticeable effect along the contacts of the 
igneous bodies. In most cases the structure of the original rock has not been altered, 
but has instead impressed itself on the new minerals developed, so that the change is a 
pseudomorphous replacement. In only a few instances has a new foliation been devel- 
oped parallel to the contact of the intruding mass. 
Unlike the effects of regional metamorphism, tb'< results at the contact of igneous bodies 
have been accomplished by more or less inte^ c chemical and consequent mineralogical 
