GEOLOGY OF SARATOGA SPRINGS AND VICINITY III 



along the western edge of the Greenwich plateau. This limestone, 

 which, on account of its Beekmantown age, now recognized, is to 

 be considered as underlying the Snake Hill shale, just below it, 

 may indicate an inverted order below the Georgian, although there 

 is a stronger probability that its presence is due to its having been 

 brought along with the Georgian along the trust plane. 



Our observations along the west edge of the Cambric area, not 

 only on the Schuylerville quadrangle but also northward and south 

 of it in Rensselaer and Columbia counties, have led us to the 

 conclusion that we have there precisely that case w^hich Dale con- 

 sidered as not an ordinary probability, and therefore would ex- 

 clude from his working hypotheses, namely, a folded thrust plane, 

 along which the Georgian rocks have everywhere been overthrust 

 over the Ordovicic rocks. This condition is, in our opinion, a 

 structural feature of the first magnitude of the entire plateau. 

 Likewise the underlying Ordovicic is not only compressed into 

 small folds from the east, but also more or less bodily overthrust 

 over the series of rocks of the Western basin. The same intense 

 pressure which only a few miles farther east caused the regional 

 metamorphism of all these shales, has to be considered as com- 

 petent to produce the folding and the extensive overthrust faulting. 



The facts which induce us to consider the entire western part of 

 the Cambric area at least as overthrust on the Ordovicic rocks, are 

 of both structural and topographic nature. The strike of the 

 Ordovicic rocks in the Saratoga plain leads these rocks directly 

 under the Cambric rocks of the Greenwich plateau, as a glance on 

 the Schuylerville map will show. While from the northeast corner 

 to the foot of Louse hill the Snake Hill beds pass under the 

 Georgian rocks, in the southeast corner of the quadrangle, north 

 and east of Willard mountain, the Normanskill rocks disappear 

 under the Georgian rocks. In several localities where rivers have 

 breached the margin of the Cambric Greenwich plateau, the Ordo- 

 vicic rocks can be traced upward along the river, forming reentrant 

 angles in the outline of the Cambric. Such a large reentrant or 

 embayment is formed by Moses kill and another broader one by 

 the Batten kill. 



Very instructive are the cases of the Hoosic river and Deep kill. 

 At Schaghticoke the Schaghticoke shale (of lowest Ordovicic age) 

 is exposed in the bottom of the river, while the hills to the north 

 and south of the gorge, in the general strike direction of the rocks, 



