127 



appear not to have a sufficiently continuous range across the 

 State to make it necessary to carry out the subdivisions of the 

 formation, as they were detailed when describing the rocks along 

 the Delaware. 



Convenience, however, recommends that we consider sepa- 

 rately the wide belt of argillaceous rocks, embraced between the 

 arenaceous ones of Scudder's creek and the still coarser ones of 

 the vicinity of Centrebridge. 



The inferior margin of this zone of strata, after passing by 

 Princeton, is prolonged to Lawrence's brook, where it consti- 

 tutes also the southeastern edge of the whole middle secondary 

 region, being overlaid unconformably along the southern side of 

 that stream by the lowest of the upper secondary series. Beyond 

 the mouth of Lawrence's brook, the same rocks extend every 

 where to the eastern boundary of the State, fringing the western 

 shores of the Raritan, of Staten Island Sound, and of the Hudson 

 river. 



The upper or northwestern margin may be traced from the 

 stream east of Centrebridge, past Middlebrook, on the Raritan, 

 and thence along the eastern base of the easternmost principal 

 ridge of trap. The occurrence, in the neighbourhood of Pat- 

 terson, of a coarse siliceous sandstone and conglomerate rock 

 resembling that near Centrebridge, and the occasional appear- 

 ance of a similar material at points adjacent to the line designated, 

 seem to mark this as a boundary not altogether conventional. 

 Within the two limits thus traced, the almost invariable aspect of 

 the rock is that of a brownish red shale, including beds of a more 

 or less argillaceous and micaceous sandstone of a somewhat 

 lighter tint, some localities of which furnish good building stone 

 and flag-stone. 



Between the Delaware and the Raritan rivers the unaltered 

 varieties of the rocks of this belt are seldom quarried, and present 

 but few features of either economic or scientific interest. 



The altered portions, important in both these points of view, 

 will be described somewhat in detail when allusion is made to 

 the several ranges of trap with which they are connected along 

 the Raritan, where, as already mentioned, occur fine opportu- 

 nities for studying this portion of the formation. 



At New Brunswick, the dip and structure of the red shale are 



