NEW ENGLAND ANTHRACITE FIELDS.
coals of the New England States are anthracite in character, and were formed under the same influences which produced the anthracite of Pennsylvania; but the geological conditions differ materially, and the in tensity of the heat to which the bitumen and carbon forming the coal were subjected in consequence, destroyed their value as a fuel.
The coal-basins of Massachusetts are found in or closely upon the gneissic rocks, and partake, in consequence, of all the imperfections which always accompany such formations.
The depreciation of the Paleozoic rocks in the northeastern limits of the ancient Appalachian Sea are almost as marked and uniform as that which notes their progress west. But in the New England States existed the granite boundaries of the great basin, and the formations of a later period only took place in the depressions of the granitic or gneissic rocks.
The coal, therefore, is peculiar, or characteristic of all such formations, —thin and irregular in its stratified beds, or subject to sudden contractions and enlargements, to upthrows and downthrows, slip dykes and rock faults, saddles, troubles, hitches, dirt faults, and all the ills of coal-basins existing without those necessary conditions for the production of coal noticed in Chapters III. and IV. of this book.
It has been stated, and partially demonstrated, that this coal really does exist in the true position of our great coal-fields, and that the sedimentary strata in which it exists have been metamorphosed by heat into the sub-crystalline; but this does not alter the effect, since intense heat only could change the rocks in this manner, as all the metamorphic or gneissic rocks have been changed by the same means.
The basins in which this coal exists are extremely irregular, and must have been always unfavorable for the even and uniform stratification of valuable coal-beds; but these unfavorable conditions have been subse quently increased in deformity by lateral contractions, which have doubled and folded the strata in sharp wares, and not only crushed the coal, but by the irregular movements of the crust caused the coal-beds—and of course the accompanying strata—to slide above or below their true horizons of connection.
We find the same cause operating violently on the value of the Pied mont and New River coal-fields of Virginia, as far as the slides and faults are concerned; but in these Southern fields the heat has not been so intense; only a small portion of their coals has been changed to anthracite ; but the anthracite is always on the side nearest the regions of heat, and the bituminous coal is always most remote.
In the anthracite coal-fields of Pennsylvania an immense thickness of sedimentary or Paleozoic strata existed between the coal and the regions of heat, and formed an even and uniform floor for the reception of the coal measures. It is possible and probable that the intensity of heat and volcanic action was far greater in the vicinity of the Pennsylvania than the New England anthracites; but the interposition of the immense shield of Paleozoic strata not only preserved the coal from actual contact and destruction, but added materially to the growth of the coal-beds by the production of the carbon and bitumen which escaped from them.
Nothing can be more evident than the fact that the salvation of our magnificent anthracite fields is due to the immense thickness of the ozoic or stratified floor upon which they rest. Had it not been for this pro tection, we should have had distorted and jumbled basins of plumbago, coal, dirt, slate, and rock. Even under the favorable circumstances in which they exist, some of our deepest and largest basins nearest the regions of volcanic heat have barely escaped its destructive influences.
In Pennsylvania, as in all anthracite basins, the hardest and purest anthracite is always nearest the point from whence the heat emanates, and the softest or semi-bituminous is most remote, but with this exception : when the coal is unprotected from the intense heat by intervening strata, it is frequently destroyed by that heat, or subsequently crushed and dis torted by the contractions of the crust when condensed by the evaporation or loss of the same, viz., heat.