ESSEX COUNTY. 275 



ten feet, and tlieir ends also bent as in the cut. This we may, widiout doubt, consider as 

 having been produced at the time of the preceding uphft, communicating in this direction a 

 wave-hkc motion to the rocks. 



Near llic plane of junction of the southern fracture, there is a trap dyke in the face of the 

 clifT, about two feet wide, which may be traced a mile in a northwest direction. Whether 

 the force required to inject this mass of volcanic matter fractured the rocks as has been 

 described, cannot be determined. I have supposed that the trenton, and the slates and shales 

 of the Hudson river, \vere borne upwards upon the chazy limestone. We do not, however, 

 find a vestige of either mass remaining, though the chazy limestone maybe traced west two 

 or three miles, and we find the other rocks on either hand as has been stated. It is not difficult 

 to reach the cause of this ; for there can be no doubt that the whole of that portion of these 

 masses thus elevated has been swept away entirely down to the hard and firm rock called the 

 chazy limestone, at least so as to form a tolerably level surface. This mass is, however, 

 some fifty feet higher than those on either side, though the latter are geologically three or 

 four hundred feet higher than the former. At this locality, then, we have two very distinct 

 kinds of changes, which have taken place since the deposition of the Hudson river shales : 

 first, an elevation of tiie strata in mass ; and secondly, a change by denudation, by which the 

 height of the surface is diminished and reduced nearly to its former level. The scale, it is 

 true, upon which these changes have taken place, is small, and confined really to a limited 

 area ; yet it is a fine illustration of the changes which have taken place since the creation of 

 organic beings, and it is the more interesting as the whole eff"ect is within the sphere of our 

 observation. 



On the south side of the uplift which has been described, there are phenomena differing 

 somewhat in character from those upon the' north, but resembling them in some particulars. 

 Several dykes, in the first place, appear in the face of the cliff, traversing the slate of the 

 Hudson river series. Some of them are in a soft decomposing state, and unlike the one 

 already mentioned in the chazy limestone a few feet farther north ; they are both curved or 

 contorted, and apparently insulated or surrounded by the slate. This is probably not the 

 case, but their position may be explained on the supposition, either that a portion of the slate 

 is broken down and washed away, which contained the part which connects whatever now 

 remains in the cliff with the mass below ; or else, the connecting part is still contained deeper 

 in tin; slate, and may yet be exposed as the cliff is broken down. Numerous veins of calca- 

 reous spar, too, appear in the cliff in parallel lines. But what is still more interesting, is 

 the shift which the strata have suffered, not, as may appear to some, by the filling of the 

 vertical veins of spar, but probably by the movement communicated to the strata at the time 

 the chazy limestone was thrust through the adjacent mass of slate. The annexed cut will 

 illustrate what has taken place, and the shifts the strata have suffered : 



