Page:Report on the geology of the four counties, Union, Snyder, Mifflin and Juniata (IA reportongeologyo00dinv).pdf/94

66 F³. as it certainly is the most important economically from the fact of its being a key or guide-rock to the location of the “Sand Vein” fossil-ore bed immediately above, and the Danville fossil-ore beds which underlie it anywhere from 10′-25′.

This remarkable sandstone is hard to describe, but once seen can rarely be mistaken for anything else. It has a dull brown to whitish-red cast, is frequently full of fossils, has a square but rugged, fracture, and sometimes is made up wholly of fragile layers only a few inches thick. It is only about 8 to 10′ thick in Union and Snyder counties along the river, though increasing to 30′ in western Snyder, where it makes a very prominent ridge wherever it outcrops.

It occurs at an interval of 150′ to 200′, say 175′ below the Bloomsburg red shale group, and about the same distance above the Iron sandstone, and as in a large part of Union and Snyder counties its dips are moderate, it creates a ridge, always quite prominent in such cases, at some distance from the base of the Medina mountains.

The Sand vein ore occurs on top of it, usually separated from the Ore sandstone by the “Sand Rock,” a coarse brownish ferruginous sandstone, evenly bedded in places 3′ or 4′ thick, elsewhere absent. This ore bed has furnished by far the largest bulk of the ore mined in these four counties, although by no means a persistent bed, either in bed section or character. Frequently it is altogether absent and again often so lean and siliceous as to be a mere ferruginous and sandy limestone, fossiliferous and not mined at all. However, where the ore is good it shows from 2′ to 3′ thick, usually divided in the center by a band of “Jack” or hard slate from 0′ to 10′ thick. It is impossible to give any typical section of this bed, for it varies greatly and within comparatively short distances. Above water level it furnishes a good quality of soft fossil ore, with 45–47 per cent. of iron in the furnace, and from .2 to .5 per cent. of phosphorus. The silica varies anywhere from 10 to 30 per cent., the percentage of iron running down accordingly.