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OF SOUTH CAROLINA. 11 
a molten state, through the superincumbent rocks, bearing them upwards in its ascent, as repre- 
sented in the section, Fig. 2. 
It sometimes happens that the protruded mass passes through without any apparent marks of 
violence. This is the case very often with trap dykes, which seem to be igneous matter barely 
injected into cracks and fissures in the rocks. It sometimes happens, however, that trap dykes, in 
their passage through other rocks, turn the edges of the strata up, as represented at ¢, Fig. 2, leaving 
evident marks of great violence. 
The origin of a force capable of such stupendous effects, has long been the subject of interesting 
investigation with Geologists. Volcanic action, from its well known effects, and from its connection 
with the changes produced by earthquakes, naturally suggests itself when we look for the cause of 
those upward movements which have taken place, on a vast scale, in the earth’s crust. 
Voleanic action, taken in the wide sense in which Humboldt defined it, as “an influence exer- 
cised by the interior of a planet, on its exterior covering, during its different stages of refrigeration,” 
does indeed include all the causes assigned for these phenomena; but in its more limited meaning 
it is difficult to conceive of its action along extensive mountain chains; and hence many Geologists 
have been led to attribute the inequality of the earth’s surface to the slow cooling down of the sur- 
face of the melted matter, beneath the solid crust of the earth, and the consequent contraction. 
This theory seems applicable, whether we consider this molten mass as forming the nucleus of 
the globe, or distributed in immense reservoirs, like seas and lakes, beneath the surface, and con- 
stantly replenished by electro-chemical action. very one who has had any experience in stone 
structures must have noticed the difficulty of preserving the cement or mortar in the joints of large 
stones, such as coping stones and door-steps. 'This difficulty arises from the annual expansion and 
contraction of the stones, owing to changes of temperature: the expansion crushing the cement, 
and the contraction leaving the joints open. 
A series of experiments was instituted by Col. Totten, to determine the amount of expansion 
produced by a known increase of temperature, which resulted in showing that granite expands, for 
1° F. .00004825 of its lineal dimensions. Mr. Lyell has calculated from this, that if a portion of 
the earth’s crusts, one hundred miles in thickness and equally expansible, were to have its tempera- 
ture raised to 600° or 800° F. it would be sufficient to produce an elevation of two or three thousand 
feet. We have, then, in the enormous force that may be exerted by expansion and contraction, 
(for they exert equal force,) a cause sufficient to account for all the phenomena of elevation and 
subsidence. 
The operation of this contraction will be rendered plain by supposing a sheet of igneous matter, 
covered by a crust, produced by the cooling of the surface by radiation. As the cooling and con- 
sequent contraction went on, portions of the crust would be drawn down to accommodate itself to 
the diminishing central mass. This would produce a subsidence of those parts, and as the crust 
became thicker and less yielding, while the cooling still proceeded, foldings, fractures, and upheavals 
would be the result. The water on the surface would be collected into the depressions, to form 
oceans, while elevated strata would appear above the surface, as islands and continents. 
The deposition of sedimentary matter at the bottom of the ocean would retard radiation from the 
heated mass, and an elevation of temperature would be the result, which would produce a corres- 
ponding elevation of these newer beds. And in this way may be explained the repeated oscillations 
