154 ^'EW YORK STATE MUSEUM 



at Newburgh a gneiss ridge is accompanied by limestone, but in its 

 southerly extension the slates are in direct contact. This relation 

 is believed to be wholly due to faulting on both limbs of the anti- 

 clines. This gneiss ridge disappears southward beneath the drift, 

 but the borings have shown that it continues across the aqueduct 

 line, although it has lost its influence on the topography. There 

 are other inliers of similar character such as Cronomer hill 3 miles 

 northwest of Newburgh. Between these two gneiss ridges lies the 

 southerly extension of the Wappinger limestone belt. But so far 

 as is known it disappears beneath the Hudson River series long 

 before reaching the line of exploration. 



Near Idlewild station, filling the space between the two branches 

 of the Erie Railroad, there is a syncline containing the series of 

 Siluric and Devonic strata which spreads southwestward to include 

 Skunmemunk mountain, an outlier of Devonic strata. This is the 

 only occurrence of these formations in this region south of the 

 Rondout valley. The structure and stratigraphic features of this 

 occurrence have been worked out by Hartnagel. Its northward 

 extension in all probability terminates abruptly by a cross fault not 

 far north of the Ontario and Western Railroad. 



From these occurrences southward to the Highlands proper 

 nearly everything to be seen through the drift is Hudson River 

 slates. 



The Highland gneisses are bounded on the north side by a fault 

 or series of faults. This brings various members of the overlying 

 series into contact along the margin. In the best place where a 

 direct observation can be made the gneisses are thrust over upon 

 the Hudson River slates along a plane that dips about 40 degrees 

 to the northeast. It is probable that a displacement of as much 

 as 2000 feet or more could reasonably be assumed at this place. 

 The contact zone also is much crushed and bears every evidence 

 of having undergone extensive disturbance of this kind. Others 

 of this same type occur within the gneisses where weaknesscb 

 formed in this way permit the development of such notches as 

 Pagenstechers gorge. In some cases the rock beneath the surface in 

 these zones is more decayed and less substantial than that at the 

 surface. 



Exploration 



The first borings made with the wash rig were found extremely 

 unreliable in the Moodna valley. That is because of the very 

 heavy bouldery drift forming the greater part of the filling on the 

 ancient topography. Next to the Hudson river gorge itself, no 



