I06 NEW YORK STATE MUSEUM \ 



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number of small ones of the character of progressive overthrusts. %% 

 In the western Normanskill area this is suggested by the pinching 

 out of the grit belt, as stated before, against the western boundary | 

 of the area. The line bounding the Willard mountain area of i 

 Normanskill rocks on the west is to all appearances of the same j 

 character, for this would explain in part that the older Normanskill ' 

 rocks project here more than looo feet above the younger Snake ' 

 Hill beds adjoining them to the west, and that we find structures, j 

 as the cross fold in the southeast corner of the sheet, cut of¥ by I 

 that line. 



If the eastern Normanskill belt is also overthrust westward, it 

 would seem to have been not only overthrust, but also thrown into i 

 the high mountain folds of Willard mountain before the oncoming 

 of the Georgian overthrust waves, for the latter were clearly turned j 

 aside by this projecting mass, as shown by the curving strike of ^ 

 the Georgian rocks northeast of Willard mountain. That it still 

 in this late time projects so boldly is of course mainly due to the 

 great hardness of the grit and especially of the white-weathering j 

 chert beds which form its backbone. 



As far as this relatively small area indicates, we have here a 

 series of successive overthrust masses, producing the intricate struc- 

 ture which in various parts of Europe is known as " Schuppen- ] 

 struktur," the separate Schuppen being pushed over each other ■ 

 like scales (Schuppen). 



While the prevailing material of the rocks that have been over- j 

 thrusted consists of shales, there are, it appears to us, sufficient ! 

 masses of solid, hard grit and chert beds in the Normanskill and 

 Snake Hill shales and of limestone and quartzite beds in the Geor- 

 gian rocks to have transmitted the stress to the shales. Also the 

 compact Bald Mountain limestone and dolomite must have been 

 important agents in the development of the overthrusts. In the Bald 

 mountain section (see page 109 and sections and diagrams in pocket) 

 the limestone is seen to be bounded by overthrust planes from the 

 shales above and below, showing that the shear followed in some 

 places the bedding planes between the limestone and shale, thus 

 separating the two. It is possible that the successive overthrusting 

 took place similarly as suggested by Bailey Willis^ for the Alpine 

 structure, although we have been led to infer from our observa- 



1 Bailey Willis. Thrusts and Recumbent Folds, a Suggestion Bearing on 

 Alpine Structure. Science, 25:1010. 



