GEOLOGY AND PxiLEONTOLOGY OF THE SCHOHARIE VALLEY 87 



from 600 feet at Central Bridge to 720 at Howes Cave bridge, 

 820 at Barnerville bridge and 900 feet at Cobleskill, or 300 feet 

 in 8 miles, i. e. 37J feet to the mile, counteracts tlie diminished 

 dip of the strata. Thus the loops around the Cobleskill valley 

 are not much longer than those surrounding the Schoharie 

 valley, even though the dip along the axis of the former valley 

 is only about 50 feet to the mile or approximately 1 foot in 100, 

 w^hereas in the Schoharie valley it approximates 135 feet to the 

 mile or about 1 foot in 40. In the case of the Schoharie valley 

 then we have a nearly level river plane intersecting a strongly 

 dipping stratum plane; in the Cobleskill valley, a moderately 

 dipping stratum plane is intersected by a rising river plane. 

 The results in either case are nearly the same. 



The valley of the Fox kill differs from the other two, in being 

 cut nearly parallel to the strike of the strata or even somewhat 

 dow^n the dip. This accounts for the difference in the character 

 of the outcrops which are nearly parallel on opposite sides of 

 the valley. The looping of the outcrops of the lower strata 

 around the Fox kill valley, which occurs some distance east of 

 the limit of the map, is here due entirely to the rise of the valley 

 floor, which successively intersects the horizontal planes of the 

 strata. Thus we have three relations of strata and river valley^ 

 all of which produce the effects of deflected outcrops, namely 



1) declining strata and horizontal valley floor as in the Schoharie, 



2) declining strata and rising valley floor as in the Cobleskill, 

 and 3) horizontal strata and rising valley floor as in the Fox kill. 



Most of the smaller streams of the region have also caused an 

 upstream deflection of the contact lines between formations. 

 This -is due to the fact that these streams generally have their 

 origin in the hills on either side of the greater valleys and have 

 cut ravines of greater or less magnitude. In these ravines the 

 contact lines are deflected but where the streams run across the 

 contact lines in the valley bottom, no such deflection takes place. 

 Not infrequently the contact line which has the most pronounced 

 deflection is that which separates a harder from an overlying 

 softer bed. The softer bed has been eaten away by the stream, 



