GEOLOGY OF SARATOGA SPRINGS AXD VICINITY IO5 



ern, and may therefore be a continuation to the present day of the 

 " progressive overthrusting " here described.^ 



There is, however, also evidence of possible larger faults, both 

 normal and overthrust, in the folded shales of the Saratoga plain. 

 One larger fault is directly observable at Ballston Spa, separat- 

 ing the Canajoharie shale and Snake Hill beds. This fault is 

 traceable southward through the Ballston lake depression toward 

 the Mohawk river. Its presence is shown by the steep eastward 

 dip of the Snake Hill beds, which rapidly decreases as one goes 

 east, the part of the Snake Hill belt between Ballston Spa and 

 the lake being but little disturbed by crumpling. From present 

 evidence we infer that an important thrust plane separates the 

 Snake Hill and associated now intensely crumpled formations of 

 the eastern basin from the relatively undisturbed Canajoharie 

 shales, along this fault line northeastward beyond the limits of 

 the map. This fault, which is probably a nearly horizontal thrust 

 fault (see diagram), is of the character of a "scission" fault or 

 *' charriage." The eastern formations have been pushed westward 

 over this plane for an unknown, but probably considerable, distance. 

 If our conclusion that the Rysedorph Hill conglomerate properly 

 comes in the upper part of the Normanskill shale is correct, then 

 its absence near the boundary line of the two on the Schuylerville 

 quadrangle would also indicate that this line is not one of normal 

 stratigraphic succession, but of diastrophism or movement of the 

 earth crust. As we have shown above, the entire shale belt is tran- 

 sected by a great number of slips or thrusts of small throw, which 

 combined might be competent to bring up the older shales in over- 

 lying position to the younger ones ; they would, however, not throw 

 the Rysedorph Hill conglomerate out of its supposed normal posi- 

 tion near the top of the Normanskill beds. 



Whatever the character of the contact along the western edges 

 of the Normanskill areas may be, it seems clear that it is in the 

 nature of an overthrust, either a single large overthrust or a 



1 Woodworth (op. cit. p. 26) is inclined to explain these small faults as step 

 faults with a downthrow to the northwest, which would produce the same 

 effect as an overthrust from the east, and to consider them as part of a tilting 

 of the land in and about the New England district, since the retreat of the 

 Wisconsin sheet, or as resulting from the lifting out of the cores of synclincs 

 through lateral pressure from the east. Since the synclines. as a rule, are 

 overturned to the west and compressed into close folds in the shale district, 

 it is improbable that the forcing out of the core of the synclines could be 

 responsible for the numerous small overthrusts observed by us. 



