Dale — Geology of the North End of the Taconic Range. 189 



The section is drawn so as to cross contacts where the uncon- 

 formity is manifest but owing to insufficiency of data, the 

 folds represented in the Cambrian portion away from the con- 

 tacts are largely hypothetical. The straightness of the Cambro- 

 Ordovician boundary on the west side may be the result of fault- 

 ing ; but as the unconformity is quite as great at several points on 

 the east side, where faulting is improbable, and as N.E. strikes 

 are quite as characteristic of the center as of the sides of the 

 Cambrian tongue, it is evident that faulting is not the cause of 

 the unconformity. If it exists, it is between rocks which were 

 already unconformable. Such a fault would have to be a 

 reversed one and would hade to the east, bringing the Cambrian 

 beds to overlie the Ordovician ones. The section has been 

 constructed to show the relations without the faulting, although 

 such faulting is regarded as quite possible. That the limestone 

 once covered at least the western border of the Cambrian, is 

 probable from the presence of the small outlier in the Hyde 

 Manor Golf grounds, already referred to and shown in the 

 section. This limestone strikes NY10E., as does also the nearest 

 Ordovician limestone east of it, but the Cambrian slate about it 

 strikes N.40E. 



The interpretation of the facts set forth in the map and sec- 

 tion is this : The Lower Cambrian slate formation, which is now 

 regarded as the off-shore equivalent of the quart zite of the 

 Green Mountain range (Vermont Formation of U. S. G. S. 

 Monograph XXIII), was folded at the close of Lower Cambrian 

 time and in places, raised above sea level, forming one or 

 more islands in the Champlain oceanic arm. The direction of 

 this Cambrian folding was generally the same as that of Ordovi- 

 cian time, known as the Green Mountain movement, but at this 

 point the axes of these Cambrian folds, for some reason, had a 

 more easterly course, resulting in N.E. strikes. A very gradual 

 depression, beginning during the latter part of Stockbridge 

 Limestone time and continuing into Hudson time, caused the 

 deposition of some of the limestone and of all the schist upon 

 these former islands of Lower Cambrian rocks. This, as sug- 

 gested to the writer by Professor C. R. Yan Hise, resulted in 

 some places in an overlapping of the limestone by the Hudson 

 schist and slate, and in others, in the deposition of the schist 

 and slate immediately upon the Cambrian slates. This over- 

 lap, in particular, accounts for the absence of the Stockbridge 

 Limestone for 50 miles along the west side of the Taconic range. 

 In 1898* the writer sought to explain this by a local change 

 from calcareous to argillaceous sedimentation during Stock- 

 bridge Limestone time, as had been proven by Pumpelly and 



* Op. cit. Slate belt, etc., p. 295, last paragraph, to p. 297. 



