420 NEW YORK STATE MUSEUM 



are in almost entire ignorance. Nor isi there any evidence as to 

 the altitude above sea level given to the region. Subsequent 

 depression and deposit on the southern flanks of the region, indi- 

 cate that much of it had slopes to the south and southwest. 

 How mu/cli effect the Taconic uplift may have had on the eastern 

 border is a question, but the possibility of a sagging along the 

 line of the Clininplain valley, implying an easterly slope to the 

 eastern part of the region-, must be kept in mind. It seems there- 

 fore likely that the original character of the region, that is a low, 

 domelike elevation, which slowly sank beneath the encroaching 

 waters of the various early Paleozoic marine invasions, till it was 

 finally overtopped, was renewed by this Postutica uplift, and that 

 the elevation was of the low dome type. Its apex, however, was 

 likely shifted from its former position in the southwest and moved 

 northeastward. Q^he ett'ect of such an uplift would be to- increase 

 somewhat the slight initial dip of the sediments outward from 

 the dome in all directions. An alternative view is that the region 

 was merely an extension of the land areas which certainly existed 

 to the north, and to the east during this time, and that it thus 

 sloped, ais a whole, to the siouthwe'st. In either case drainage 

 Avould set up on the mew surface, and would consist at first prin- 

 cipally of streams Avliich flowed down the sloping surfaces, or 

 across the strike of the underlying rock beds. As they cut valleys, 

 tributaries would commence to- form, and these would adjust 

 themselves to the rock beds, developing mainly on the weakest 

 and flowing along their strike. With further uplifts, if such 

 occurred, tliese would tend to extend themselves at the expense of 

 the sm'aller original streams and lead them off as tributaries to 

 the larger ones. 



The Paleozoic cover on the old Precambric floor could not 

 have been thick over the central portion of the region, and would 

 likely have been first cut through there, reaching the resistant 

 Precambric beneath. The area thus exposed would slowly 

 increase in size, faced constantly on all sides by the retreating 

 margins of the overlying rocks. These not only were of unequal 

 resistance, but ])rogresisively increase in resistance downwards. 

 Thus the Utica is weaker than the Trenton, that than the Beek- 

 mantowu', while the Potsdam is most resistant of all to wear. 



