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North of Plainfield, the red shale occasionally shows itself be- 

 tween the first and second trap ridges. A clay is found here of 

 which good bricks are made. In the next little valley northeast of 

 this, and still between the first and second belts of trap rock, and 

 north of Scotch Plains, the red shale is well exhibited along the 

 banks of the stream, presenting a low but regular escarpment 

 in the hill side. About the middle of these beds of shale, and 

 running parallel with them throughout the whole face of the rock, 

 is a thin belt of limestone, a material of unusual occurrence, 

 particularly in this central portion of the formation. 



It is thinly bedded, in layers varying from an inch to six inches 

 in thickness, constituting together a bed between one and two feet 

 from lop to bottom. 



On the other side of the stream, in the northern face of a deep 

 ravine, a similar, in all probability the same, bed of limestone is 

 exposed for a considerable space. It is more massive than at 

 the other spot, being a solid seam between two and three feet in 

 thickness ; above it and beneath it occurs the ordinary red shale, 

 the whole dipping to the northwest, at an inclination of about 12°. 

 The upper beds of shale along the whole valley, are here very 

 regular, but in the bottom of the ravine above mentioned, the 

 trap seems to have invaded the strata, inducing considerable 

 confusion. Besides producing much alteration in the shale and 

 sandstone, it has in places modified the limestone, giving rise to 

 a mass of white semi-crystallized carbonate of lime. These 

 unusual features, so easily understood by science, have led to 

 several fruitless mining enterprises in this neighbourhood. 



On the northwestern side of the mountain, near the road from 

 a paper-mill, there is a quarry of slaty sandstone, furnishing an 

 excellent fiag-stone. It is also used for tombstones, being both 

 neat and durable. It exhibits signs of having been baked by an 

 adjacent dike of trap. 



Following the course of the Passaic, from Chatham to the 

 semicircular valley enclosed by the Hook Mountain, (laid down 

 on the map as Towakow Mountain,) we pass over a wide and 

 nearly level tract of almost uninterrupted diluvium. But in the 

 recess of the Hook Mountain, the red sandstone sometimes 

 appears along its southeastern base. 



About one-third the distance from its eastern to its western 



