TIN MINING DEVELOPMENTS. 45 
seems probable that, subjected to the action of solutions during long geologic ages, the 
cassiterite may have been in great part dissolved and carried away in the streams. It is 
not unlikely that the peculiar conditions existing when the country was reduced almost to 
base-level had much to do with this result. The streams, then being sluggish, could dis- 
solve greater amounts of chemical substances and thus become more powerful reagents 
than under ordinary conditions, and it is easily conceivable that under these circumstances 
the cassiterite was dissolved at a comparatively rapid rate. 
It has been sought to test this hypothesis by examination of individuals of cassiterite 
in the upper part of deeply decomposed dikes to see if they have suffered any etching or 
solution. The almost complete absence of smooth crystal faces and the uneven but not 
very rough surfaces of the grains have made it impossible to decide this question with 
certainty, but it seems probable that some solution has taken place. a The increased fria- 
bility of the mineral near the surface may be some indication of solution along cleavages 
or minute cracks. Furthermore, this very friability may have aided in the removal of the 
tin, both by exposing greater surfaces and in this way hastening solution and by subjecting 
the larger grains to comminution under moderate impact and thus allowing stream trans- 
portation of the fine particles. 
According to this explanation the float tin which has been found must be of comparatively 
recent derivation. Such seems certainly to be the case. No cassiterite is known at any 
great distance from deposits in place, and that which has been found is usually rough and 
angular, often found adhering to pieces of the pegmatite rock, indicating that it has been 
transported only a short distance, and that little decomposition has taken place. 
In spite of these conclusions, more systematic and extended search for stream tin is 
advocated. Prospecting by means of the pan is so easily and cheaply accomplished, and 
winning of tin from placer deposits is so much less expensive than from veins, that a moder- 
ate expenditure in search of such deposits seems to be worth the risk. 
CONCLUSIONS. 
From the foregoing remarks on the placers and the genesis of the ore, it is possible to 
draw certain conclusions which may be of interest and value to those engaged in the exploi- 
tation of these deposits. It has been shown that the present surface is, relative to the rocks, 
far below the surface existing when the pegmatite intrusions occurred and hence exposes 
portions of the ore bodies which were formed only at great depth. In other words, the 
deposition of the ore now found is in no way related to the present surface and probably 
was only remotely connected with the original surface. No solution of the tin from upper 
parts of the deposits and redeposition in lower parts — the phenomenon known as secondary 
enrichment — has taken place. The igneous origin of the ore and the fact that the deposits 
now known were themselves deep seated unite with the foregoing facts to establish the 
prediction that the deposits will probably maintain their present characters and richness 
beyond the depth to which economic mining is now possible. 
MINING DEVELOPMENTS. 
LOCALITIES. 
A condensed account of early development operations in the Carolina tin belt has been 
given in the section devoted to history (pp. 32-34). Time was not available for a careful 
examination throughout the tin belt and attention was directed chiefly to those places 
where a considerable amount of development work has been done. For the sake of com- 
pleteness, however, a list of properties on which tin is known to have been found is given 
here. A more extended account of some of these occurrences is given in Pratt and Ster- 
rett's bulletin on the Carolina tin deposits, b Prospecting has been rewarded by the discovery 
of cassiterite float at the localities or on the properties of the persons named in the following 
«Cf. p. 42. 
b Bull. North Carolina Geol. Survey No. 19, 1904, pp. 22-30. 
