GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 93 



many points between or along the strike to the north and south, and 

 along the New York Central Railroad track. The coarser, gritty 

 members, or conglomerates, were noted about midway between the 

 strikes of the two bands of red slates. 



The red slates suggest that they were formed under conditions of 

 regular exposure to the atmospheric influences, perhaps on extensive 

 tidal flats or river deltas. It is probable that these rocks were formed 

 on a gently subsiding sea floor which occasionally allowed for partial 

 nonmarine conditions of sedimentation. The relative horizon of the 

 red slates is indeterminate, but is probably not far from the base 

 of this formation. This is indicated by the geographical associa- 

 tions with the conglomerate and their absence northwest of the 

 Wappinger creek limestone. 



North of Camelot, along the railroad track, almost to Pough- 

 keepsie, crushing has affected all members much the same, producing 

 coarsely splintered slates. The great confusion exhibited by the 

 slates about Poughkeepsie and on the west of the river north and 

 south of Highland seems to have been due very largely to the effect 

 of heavy beds interbedded with thinner ones. 



Along the western bank of the Hudson from Marlboro to a 

 point two miles or so north of Highland, the rocks are quite similar 

 to those along the east bank. Westward from the Hudson the rocks 

 grow prevailingly coarser. The section along the Central New 

 England track between Highland and Lloyd shows thick masses of 

 quartzitic rocks interstratified with coarse grits and conglomerates. 

 The latter form relatively thin beds, perhaps from six to eight feet 

 in thickness, often with pebbles from two to four inches in their 

 longest diameters, embedded in a matrix of finer conglomerate; 

 while in the grits are scattered pebbles ranging from the size of a 

 walnut to that of a man's head. These coarser types prevail along 

 the track west of Highland station and are particularly well shown 

 just east and west of the overhead trolley bridge on the New Paltz 

 road and at the foot of the mountain along the road just south. 

 These rocks appear to be the northward continuation of the rocks 

 of " Illinois mountain." That some of the strata were deposited 

 under m.arine conditions is indicated by the fossils that have been 

 discovered on the eastern slope of "Illinois mountain" and on 

 Marlboro mountain farther south. While this is true, there 

 appears to have been a gradual coarsening of sediments westward 

 which suggests changed conditions in the source of supply, lying to 

 the eastward, as though terrigenous sediments gradually encroached 

 westward and contended with marine deposits. This idea would 



