Page:Popular Science Monthly Volume 13.djvu/666

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THE POPULAR SCIENCE MONTHLY.

stratified rocks. Cooling in place, these trap-sheets are now conformable to the associated strata, and seem at first sight to be normal portions of it, but the metamorphism which they have produced in the beds above and below them show that they are intrusive. The erosion which has since acted upon the surface of this region has cut away the softer sandstones and shales, leaving the outcropping edges of the trap-sheets in high-relief, and these are now known as the Palisade Range, First and Second Newark Mountains, etc.

It has been suggested that the New Jersey and Connecticut basins were once connected by strata which occupied all the interval between them, and that by the subsidence of the sides or the elevation of the central portion an arch was formed the crown of which has been removed by erosion. It seems, however, scarcely probable that some thousands of feet of Triassic rocks, including thick beds of hard and resistant trap, should have been so completely carried away from the interval of 100 miles now separating the Triassic basins, that not a trace of them should be anywhere left. There is apparently good evidence also that the trap-sheets of the Connecticut Valley issued from fissures there, and appertained to a distinct line of disturbance; and, further, that the materials composing the Triassic series in each belt were derived from the adjacent highlands, and were spread by currents which swept up and down two narrow troughs.

To some persons, the most interesting fact in regard to the Trias yet remains to be mentioned, and this is that from the quarries sunk in its sandstone-beds—of which the most important are at Bellville, New Jersey, and Portland, Connecticut—has been taken the brown-stone to which we owe the architectural beauty and monotony of the best portions of our city. Copper is also frequently found impregnating the Triassic rocks, but it has generally proved only a snare to those who have attempted to work it, the deposit being small and unreliable.

PSM V13 D666 Profile section from trowbridge mountain to the hudson river.png
Fig. 2.

During the time in which the Jurassic rocks were deposited in other places, the Atlantic coast of North America seems to have been above the sea-level, for we find here no strata which are certainly of that age. Some writers have called Jura-Trias the beds described as Triassic on the preceding pages, but up to the present time no facts have been brought to light which justify this usage. Possibly the uppermost beds of the series may hereafter be found to contain Jurassic fossils,