OF METALLIC VEINS AND BEDS OP VALUABLE MINERALS. 43 
cal attraction, are said to be more susceptible of disintegration 
than the primitive. They also more frequently contain lime. 
Where this earth is present, the fertility of the soil created, will 
depend upon the relative proportion of the other ingredients of 
the rock. Thus a gray-wacke containing lime, and in which the 
argillaceous cement is abundant, will form good land. But where, 
as in the case of the sandstone lying east of us, the rock is an ag- 
gregate of particles of silica, held together by a cement without 
lime and small in quantity, the soil arising from its decomposi- 
tion, will be light and unproductive. Clay-slate is said to form 
a tough strong soil, which retains whatever it receives ; but in 
North Carolina it is only where a rock considerably removed from 
pure argillite is found, that there is good land within the limits of 
the transition formation. 
3. The secondary and tertiary strata, having only a moderate 
degree of consolidation, and a position very often approaching to 
the horizontal, the character of the soils proceeding from them, 
will depend almost exclusively upon their composition. The fer- 
tility of the alluvions of rivers, is to be ascribed in a considerable 
degree to the fact of their being highly charged with decayed 
animal and vegetable matter, but the relative proportion and fine- 
ness of their component earths, are to be regarded as important 
concurrent causes. 
OF METALLIC VEINS AND BEDS OF VALUABLE 
MINERALS. 
26. There is another subject connected with the rock forma- 
tions of the earth, which awakens in the minds of many persons, 
even a livelier interest than the one to which we have just been 
attending. It is that of metallic veins and mineral beds embrac- 
ing valuable ores and other fossils, in relation to which a number 
of facts of a miscellaneous character, and not admitting of much 
classification or reference to general principles, are to be stated. 
The mineral substances that are sought after with so much 
eagerness, by reason either of their important applications in the 
arts or the exchangeable value in commerce which immemorial 
usage has conferred upon them, occur in four different varieties 
of circumstance and situation. 
1 . In veins traversing other rocks. 
2. In beds between two contiguous strata. 
3. Disseminated through a whole rocky mass. 
4. In situations into which they have been transported from 
their original repositories by running water. 
The valuable metals, whether native or combined with a 
mineralizer, are generally obtained from veins or from such 
situations that there is reason to believe they were originally 
derived from them. Manganese and iron frequently, and some 
of the other metals rarely, occur in beds. The whole mass of a 
