36 GOLD AND TIN DEPOSITS OF SOUTHERN APPALACHIANS. 
body, to bands probably 30 or more feet wide. One of the wider bodies occurs about aj 
mile southeast of Kings Mountain village. 
While conveniently designated as dikes, these masses are in many cases much more 
irregular than the form commonly implied by that name. In strike, dip, width, and extent 
individual bodies exhibit great variations. Forking or branching is rather common. 
Many of the dikes pinch out completely, in some places being succeeded by other lenses] 
farther along in the same plane or in a near-by, parallel plane, while in others no continuation 
is found. These variations take place both horizontally and vertically. For instance, a 
dike which has a considerable continuous extent on the surface may pinch out at a com- 
paratively small depth, perhaps to be found again directly below or at one side, or not at! 
all. Conversely, a dike which is short horizontally may extend downward for a long dis- 
tance without interruption. On the other hand, a few dikes appear to be fairly regular 
and persistent so far as explored, but some of these will probably exhibit irregularities at! 
greater. distance or depth. 
A few exceptions to the general rule of conformity of the pegmatite dikes to the structure 
of the inclosing schists are worthy of notice. Exploration has not been sufficient to admit 
of very extended generalizations concerning most of the features of these tin deposits, andl 
especially is this true in regard to structure, on which conclusions can be reached in no 
other way than by a large amount of development. Such observations as have already 
been made, however, point to the conclusion that those comparatively few dikes which 
fail to correspond in strike and dip with the surrounding rocks, but instead cut across the! 
structure of the schists, are fairly persistent and regular. 
An explanation of the irregularities of those dikes which conform with the foliation ofl 
the country rock might be found in the supposition that faulting or shearing had divided 
originally continuous bodies into a number of irregular masses and lenses. But the field! 
evidence is against such a supposit ion. Slight faulting since the introduction of the pegmatite 3| 
has occurred in some places, and some of the pegmatite shows that it has been subjected! 
t o very moderate crushing, but no great amount of movement can have taken place. More-j 
over, any faulting which would affect those dikes which parallel the schistosity would also*; 
affect the cross dikes; but the cross dikes are fairly regular and can not have suffered muchl 
dislocation. 
One is therefore forced to the conclusion that these, pegmatite masses owe their present 
form to the nature of the original cavities which they filled, or at least to that of the planes 
along which they forced their way and ascended. It will thus be necessary to consider the 
character and origin of these planes in arriving at an explanation of the forms which the 3 
pegmatite bodies possess. 
We have here a region of rock beds of heterogeneous composition so folded that the form 
of any single bed may be likened to that of a piece of corrugated iron. This folding was 
produced by an enormous compressive stress acting during a long interval approximately 
at right angles to the axes of the corrugations or folds which were produced. The fold, 
however, is only the end product of a complicated process. To accomplish it there had to 
be movement among the beds and portions of the beds. This movement was a slipping or 
gliding, generally parallel to the bedding planes, and is evidenced to-day by the schistosity 
or foliation of the rocks. That these planes along which cohesion was overcome so that - 
movement could take place are planes of weakness is proved by the cleavability of the rock 
along planes parallel to the schistosity. But, as may be seen from an examination of a 
specimen of these schists, the planes of weakness are not uniform; some are more prominent 
than others, and even the most prominent ones are irregular and not continuous, but instead 
give way to others which then themselves become prominent as such planes of weakness, j 
It thus appears that the directions or the loci of greatest weakness — those places which 
would determine the position and the form of intrusion — are not simple planes, but are 
instead comprised of series of parallel planes of irregular extent, arranged more or less step- 
wise, in some places branching, in others overlapping, and in still others almost separated by 
