96 



slate formation of the valley. Near the Delaware, the common 

 limit of the slate and the overlying sandstone of the mountain is 

 seen at a moderate elevation above its base; but in Sussex, 

 between Culver's Gap and the State line, the slate rises upon the 

 eastern slope of the ridge almost to its summit, giving a fertile 

 soil to the side of the mountain, and presenting, in a long line of 

 cultivated farms, a landscape full of pleasing and picturesque 

 beauty. 



Composition and structure of the rock. — The ordinary character 

 of the third formation of the Appalachian system, as it prevails 

 in New Jersey, is that of a dark blue argillaceous slate ; it is, 

 however, very various, both as respects its colour and com- 

 position. It occurs in belts of almost every hue, black, blue, 

 dark gray, bluish gray, dingy olive, dull brown, and even some- 

 times yellow. 



It exhibits every grade of relative fineness and coarseness of 

 texture, from that of the finest grained roofing slate, to that of a 

 rough argillaceous sandstone. 



At its junction with the subjacent limestone, its beds are often 

 almost black, and more or less calcareous, while the contiguous 

 upper layers of that rock partake in some degree of the argil- 

 laceous composition and structure of the slate. Near its upper 

 limit, in like manner, where it and the gray sandstone of the 

 mountain are in contact, it acquires a somewhat arenaceous 

 texture, and in certain layers passes to a gray argillaceous sand- 

 stone. 



Nearly all parts of this extensive formation, which is evidently 

 of very great thickness, present that highly curious feature of 

 structure denominated cleavage. This remarkable tendency of 

 the mass to split into thin plates by planes of cleavage, which 

 preserve a uniform direction and inclination over extensive tracts, 

 independently of all variations in the texture of the rock, and of 

 all changes in its dip, is a feature which belongs to many of the 

 ancient slate rocks, both of the old and new continents; but in 

 few regions can it be studied on a more extensive scale than in 

 the Kittatinny Valley, where it is visible for a great distance on 

 both sides of the Delaware river. While the beds of slate through- 

 out a large portion of the northwestern belt dip towards the base 

 of the Blue Mountains, or to the northwest, and while those of the 



