94 NEW YORK STATE MUSEUM' 



seem to fall in line with what we know of the record of closing 

 Ordovicic time in eastern North America. 



Some of the members of the slate formation on the west oi the 

 Wappinger limestone belt may be much younger than those on the 

 east of it. They may be thought of as having been preserved partly 

 on account of their occupying, in general, a downthrow position 

 with reference to a tendency to thrust and reversed faulting to the 

 eastward, as well as on account of being west of the axis of maxi- 

 mum folding. 



About two miles north of Poughkeepsie are strata of black, some- 

 what carbonaceous slates in which graptolites have been found. 

 They indicate changed conditions of sedimentation from those 

 which chiefly prevailed during' the accumulation of these r':>cks. 

 These black slates have been thought to be of Utica age. 



Structural features. AMiere the stratification dip has "Seen 

 determined on what is plainly the lim]> of a fold, it is chiefly east- 

 ward. Judging from the conditions shown in the Fishkill limestone, 

 the structure is that of minor folds within a system of larger ones 

 with a tendency to overturning. The presence of strong cleavage 

 usually obscures everything in surface outcrops. 



The dimensions of the larger folds seem to be smaller at the 

 north and northeast than at the southwest, and the folds seem to be 

 more open at the north. The slate ridge just east of Freedom Plains, 

 which ends abruptly at the south at a point due east from that 

 hamlet, has synclinal structure of a rather open character. At 

 various points along the southern portion of its eastern slope it 

 shows the slates dipping to the west into the hill. To the north, 

 along- the south road from ]\Ioores JNIill to Pleasant A'alley. the 

 red slates come up on the western limb of this syncline and about 

 three-fourths of a mile farther northwest they appear again appar- 

 ently on the western limb of the succeeding anticline. 



There was a tendency to form irregular folds. This is shown on 

 a small scale in plate i8, in which we have a small overturned and 

 compressed syncline on the right of the picture, followed by an 

 irregular anticline, which becomes compressed and pushed up at 

 the west, and then another compressed syncline not distinct in the 

 photograph but similar to the first. In this instance, it is seen that 

 the production of anticline and syncline in the middle part of the 

 ledge has been incomplete. With similar tendencies prevailing in 

 the larger folds, it is easy to see how, along the western portion of 

 the irregular anticline, there would have been a tendency to over- 

 thrust. Crumpling is not uncommon. The wrinkles vary from 



