GEOLOGY. The great Arcluean belt which forms the entire eastern flank of the Appalachian system from Alabama to Canada crosses the southeastern corner of the State in a band about 50 miles wide and consisting chiefly of gneisses with tracts of serpentine. It is exposed in two sections. one ending in a point near Trenton, and broadening southwestward along the Delaware, forming the hills near Philadelphia, the other running southwest from the confluence of the Le high River with the Delaware, and forming the South Mountain chain. Between these two out crops the Archtean belt is crossed by a band of Triassic red sandstone, which runs northeast ward and extends across New Jersey. Both this and the Archaean belts are crossed by numerous dikes of trap-rock. Against the western flank of the South Mountain rests the lowest stratum of the great Paleozoic series which covers the entire remainder of the State as well as the whole of the Ohio and Upper :Mississippi Valley. On the western plateau these strata lie nearly horizontal, hut in the Appalachian uplift they are much tilted, folded, and broken, so that they outcrop in narrow successive bands. Here the hard sand
stone strata generally form the ridges, while the softer limestone forms the valley floors. The series begins with a narrow belt of Cambrian run ning along the edge of the Archtean outcrop. West of this, between the South and the Blue or Kittatinny Mountains, the Kittatinny Valley runs across the State as a belt of Lower Silurian limestone, from which rise the Appalachian ridges of Devonian rocks, with some belts of Silurian. The great Devonian area of southwestern New York extends across the whole length of the boundary, and is especially prominent in the northeastern part of the State. It is overlaid with Carboniferous strata, which, with the ex ception of the Triassic belt in the east, is the most recent formation in the State, and covers the en tire southwestern and west central regions, with isolated patches east of the Susquehanna.