ABSTRACTS AND DISCUSSIONS OF PAPERS 107 



RECTILINEAR FEATURES IN THE EASTERN CATSKILLS 

 BY GEORGE II . CHADWICK 



(Abstract) 



It seems to have escaped notice that there is in the eastern Catskill Moun- 

 tains a series of right-line valleys gridironed across the ranges in a direction 

 15° east of north similar in character to those features in the Adirondack^ 

 that have been interpreted as due to block-faulting ; but no proof is at hand 

 that such faults exist in the horizontal red beds of the Catskills. The valleys 

 indicated are, however, parallel with the mural front of these mountains facing 

 the Hudson Valley and with the strike ridges of folded Helderberg limestones 

 in that valley, a few miles distant. The field evidence suggests that the cause 

 of these features is a close spacing of joints along zones at intervals. 



Presented in abstract extemporaneously. 



Discussion 



Mr. John L. Rich : Mr. Chadwick has presented a very interesting paper, 

 and with his primary thesis I am heartily in accord. With regard to the 

 straight mural front of the Catskills, which is interpreted as probably a product 

 of glacial erosion, I wish to suggest the alternative hypothesis that, since it 

 parallels the folding in the Hudson Valley to the east, it may be rather a 

 structural feature representing the eastern limit of the flat-lying beds. 



The speaker suggests that the roughly accordant, flat-topped summits of the 

 higher Catskills may be remnants of a peneplain, possibly Jurassic. Without 

 specifically opposing this proposition. I wish to give expression to my increas- 

 ing distrust of the verity in regions of horizontal rocks, particularly where 

 some beds are distinctly more resistant than others, of peneplains for which 

 the only evidence are small flat areas on the summits and accordant altitudes. 



Dr. W. J. Miller : In the eastern Adirondacks there are numerous normal 

 faults, proved to be such by most of the familiar criteria for the recognition 

 of faults. In many other cases, however, there are prominent zones of ex- 

 cessive jointing, often showing more or less evidence of faulting by the slicken- 

 side. fault breccia, etcetera. In other cases such evidence of actual displace- 

 ment is lacking. Many times it is difficult to decide whether a given zone is 

 due simply to excessive jointing or whether the jointing has accompanied 

 actual faulting in the zone. 



Doctor Chadwick replied to Mr. Rich as follows : The peneplains bevel 

 across the rock layers, and consequently are independent of the harder layers 

 except for short intervals. 



Doctor Chadwick replied to Doctor Miller as follows : There is no question 

 of the existence of faults in the eastern Adirondacks, but it is unsafe to assume 

 that all similar rectilinear valleys are of fault origin, and particularly in the 

 northwestern Adirondack region, where the work of Doctor Martin fails to 

 find faults, although the physiographic features are similar. 



