50 



eastern base of the Musconetcong Mountain, past Vansickle's to 

 Pattensburg, reappearing again within a few miles of the Dela- 

 ware, and extending to the river. 



The small isolated range of this limestone in Mendham Valley, 

 forms the only remaining tract of the formation in the State. It 

 occupies the bottom of the valley, lying between the base of the 

 Mine Mountain and the Trowbridge Mountain, and first shows 

 itself about a mile east of Mendham, from whence it extends to 

 near the mill, which is a short distance below the village. There 

 it disappears beneath the overlying beds of the middle secondary 

 red sandstone series, which repose unconformably upon it. It 

 soon emerges again from beneath this covering, and may be 

 traced nearly from Ralston's to the Pepack Brook. 



Composition and Structure of the Rock. — This rock possesses 

 a remarkable diversity of aspect and composition. It assumes 

 almost every variey of lint, from a deep blue, almost approaching 

 to black, to the lightest shades of gray; but its prevailing colour 

 is a soft grayish blue. It is equally multifarious as to texture, 

 presenting every possible gradation, from an almost crystalline 

 character, to the closest and finest earthy aggregation of the 

 particles. When the latter character is associated with a clear 

 tint of blue, and with a sharp, smooth, well-defined and conchoidal 

 fracture, the rock usually consists of pure carbonate of lime ; while, 

 on the other hand, a rougher texture, a duller tint, and a more 

 irregular surface of fracture, indicate the presence of other 

 materials. 



The extraneous ingredients which most abound, are carbonate 

 of magnesia, alumina, and silica; while oxide of iron and carbon 

 also frequently enter into its composition, but in less proportion. 

 Tlie rock is sometimes sandy, especially in the lower part of the 

 formation; and it is frequently in other portions more or less 

 argillaceous, in which case it is apt to present a partially slaty 

 structure. It is also thin-bedded or flaggy, but oftener occurs in 

 layers of from several inclies to a loot or more in thickness. 



Throughout a large portion of the geographical range of this 

 rock, it exhibits in a greater or less degree, the oblique cleavage 

 planes, so conspicuous in many belts of the slate, which adjoins it. 

 As this interesting subject of the cleavage of rocks will be consi- 

 dered more in detail when discussing the geological features of 



