GEOLOGY OF SARATOGA SPRINGS AND VICINITY IO7 



tions that the uppermost thrust plane, that of the Georgian, is the 

 youngest, while Mr Willis considers the lowest, the great major 

 thrust G of his diagram as the youngest. 



The appearance of a narrow belt of Schaghticoke shale bet\yeen 

 Schuylerville and Thomson is evidence of a fault in that section, 

 for since the Schaghticoke is separated by the considerable thick- 

 ness of Deep Kill shales from the- Normanskill shale and these are 

 absent at Schuylerville,^ a single anticline would not explain the 

 occurrence. It is either a mass, entirely separated from its roots 

 in the contorted and crumpled shale mass, or a small fault block 

 thrust through the other shales. Glose by is the " Northumber- 

 land volcanic plug," which also is cut by slickensided planes strik- 

 ing in the general direction of the faults of the area; and which, 

 according to Professor Cushing's investigations, may be a similar 

 small block, torn off its main mass and carried forward with the 

 shale masses of the " Decke."- 



The structure of the Greenwich plateau. The Greenwich 

 plateau enters the Schuylerville quadrangle from the east with a 

 belt only i to 2 miles wide. We have to distinguish two structures 

 in the part of the plateau with which we are concerned, namely, 

 the Willard Mountain syncline and the Georgian overthrust mass. 



1 Willard Mountain syncline. We have mentioned above that 

 the imposing and historic Willard mountain, which rises boldly 

 more than 1200 feet above the bed of the Hudson river, presents 

 the structure of a syncline, much larger and more open than the 

 synclines observed in the shales of the Saratoga plain. This open 

 structure is obviously due to the presence of a great amount of 

 grit and silicious, cherty shale in the strata folded there. At the 

 northeast end the strike of the beds swings around from northeast 

 to northwest, suggesting that the syncline terminates here ab- 

 ruptly with a well-rounded curve. At the eastern foot of the 

 mountain a coarse conglomerate forms the crest of a small anticline. 



2 Georgian overthrust blanket. If one wanders from the 

 Hudson river, for instance at Thomson or Clark Mills eastward, 



1 We omit here the distant possibility that the Beekmantown beds could be 

 absent in the series at Schuylerville, although it has been claimed that they 

 are intermittent. 



2 Since " blanket " corresponds to the German " Dcckc " and means a cover, 

 relatively thin, such as these thrust masses are, they might be called " thrust 

 blankets." The word "sheet" would be liable to confusion. The French 

 "carriage" is also transferable, although the meaning of the English word 

 carriage for "that which is carried" has become archaic (Webster). 



