I02 NEW YORK STATE MUSEUM 



small overthrusts in the Canajoharie shale occur at the dam at 

 Fort Edward. Here the shale is already somewhat contorted and 

 folds that are inverted to the northwest are exposed. The entire 

 mass of rock is, however, cut by a great number of slip or over- 

 thrust faults, dipping southeast at 12° to 14°. The throw is always 

 very small and the thicker and harder beds in the shale are seen 

 to be broken by the slip planes, the upper part being thrust for- 

 ward a little over the lower, the whole suggesting surface thrusts. 

 These small slips and folds in the eastern margin of the flat shales 

 of the western basin were produced either below the overriding 

 eastern rock masses or in front of them. The step faults prevail 

 therefore in the western part of the belt and the slip faults in the 

 eastern. 



At Hudson Falls, a few miles north of the Schuylerville quad- 

 rangle, the Canajoharie shale, in being pushed northwestward be- 

 fore the eastern rock masses, appears to have encountered some 

 resistant body which twisted the shales ; they are here shattered 

 and filled with a great profusion of calcite veins. It seems as 

 if the spur of limestones and dolomites that protrudes through the 

 shales a mile farther west, at Glens Falls, had been this resistant 

 boss. 



Folded area. The structure of the folded area is of the most 

 complex character imaginable. It will be discussed in two parts, 

 (i) the structure of the Ordovicic shale in the Hudson River 

 plain, (2) the structure of the Georgian rocks and associated Or- 

 dovicic formations in the eastern (Greenwich) hill region. 



The shale belt of the Hudson River plain in the folded area 

 consists principally of the Normanskill shale in the middle and 

 the Snake Hill shale on both sides. This entire mass is uniformly 

 thrown into a mass of closely packed, small closed folds that are 

 asymmetric and uniformly overturned or inverted to the west, 

 so that on the surface and in sections where the tops of the 

 anticlines are eroded away, the entire mass has an isoclinal struc- 

 ture, all beds dipping to the east with varying angles, averaging 

 about 70°. This is especially true where only shales are involved. 

 Where, however, more resistant beds, especially the grit beds, are 

 present, these appear to be folded into less compact or closed folds, 

 and they are liable to form broad open folds in one place and 

 recumbent ones in places near by, as on Snake hill. In the Rocky 

 tucks each leg of the inverted anticline forms, as a rule, a ridge 

 by itself, the roof or top of the anticline being broken out. These 



