GEOLOGY OF SARATOGA SPRINGS AND VICINITY IO9 



Taconic ' are there pushed over on to the Chazy Terrane, and that 

 the ' Upper Taconic ' is not unconformably subjacent to the latter 

 or to the Calciferous sandrock." 



The fossiUferous Hmestone of the downthrow block is Beekman- 

 town; the lower, darker dolomitic beds belong to the same forma- 

 tion with the upper, lighter, purer limestones, being separated at 

 Bald mountain by an inthrust wedge of shale and conglomerate. 

 The black slates which Emmons considered as the Taconic black 

 slates underlying the " calciferous sandrock " are the Snake Hill 

 shales, and his conception of the structure of Bald mountain has 

 thus become completely reversed. 



The Bald mountain section is of great interest, not only in 

 regard to the Taconic controversy and the different explanations 

 offered for it, but especially as distinctly showing an overthrust 

 of the Georgian rocks upon the Ordovicic beds and the thrust- 

 shattered condition of all the beds involved in the section. The 

 photographs on plates 12-14 show the limestones much broken by 

 thrust planes auxiliary to the master overthrust, and overlain by 

 masses of mylonite (see page 84) upon which rest the Georgian 

 shale and shaly limestone. There remain standing detached cliffs 

 or blocks consisting of conglomerate and shale on the south side 

 and in front of the quarry, which indicate the former extent of 

 this formation, while to the southwest and west of the quarry 

 there outcrop in several places the dark dolomites (see diagram 

 of front of mountain, plate of sections). It thus appears as if 

 the shales and conglomerates separate the pure limestone above 

 and the dark dolomite below. As we have stated in another place, 

 these two divisions both north and south of Bald mountain grade 

 into each other and form one formation. It is therefore probable 

 that the shales and conglomerate in front of Bald mountain form 

 only a wedge thrust in between the limestones and dolomite. 



Dale {op. cit., page 293), from his elaborate investigation of the 

 Xew York-Vermont slate belt, arrived at the conclusion that the 

 overthrusting at the western margin of the Cambric area is only 

 local in the shale region of New York- Vermont. He says : 



The striking features in all these localities, leaving out the last, are the 

 uniformity of the dip, the great thickness of the Lower Cambrian, and 

 the thrusting over of the latter on the Trenton. These features imply great 

 rigidity in the beds and relief of compression through faulting. These, how- 

 ever, are just the features which are wanting along the slate belt. The 



