﻿2J2. NEW YORK STATE MUSEUM 



prevalence of Siluric and Devonic strata, i. e. all strata above the 

 Hudson River slates. These strata have been affected by only one 

 great mountain-making movement — that of the Appalachian fold- 

 ing, and minor disturbances of still later date. 



B Hudson river district. This includes that portion of the 

 region lying between the northern border of the Highlands and the 

 Shawangunk mountains. It is marked by the prevalence of Cam- 

 bric and Ordovicic strata, i. e. Hudson River slates, associated with 

 Wappinger limestone and Poughquag quartzite as the chief bed 

 rock. These strata have been affected not only by the Appalachian 

 folding but also by a still earlier one — that of the Green mountains 

 and the Taconic range. They were folded into mountain ranges 

 and worn down in part again before the Siluric and Devonic strata 

 of district A were in existence. Therefore as a structural problem 

 this district (B) is approximately twice as complex as the other. 



C Highlands district. This includes all of the region com- 

 monly known as the Highlands of the Hudson as well as the rest 

 of the area south of the Highlands proper to New York city. Its 

 rocks are the oldest — much the oldest. They had been folded into 

 mountain structures and in part worn down before any of the 

 others were accumulated. They have also suffered extensive 

 igneous intrusion so that in places these igneous types prevail. 

 And besides they have been metamorphosed far beyond the point 

 of any other group. No other series of strata has been so pro- 

 foundly affected. They form the lowest group. All things con- 

 sidered this district should be structurally three times as compli- 

 cated at the first one (A), and adding the igneous and metamorphic 

 complexities, it is probably more near the truth to consider this 

 Highland district four or five times more complex. 



All of the formations from the oldest to the Middle Devonic are 

 involved. For the specific formations and their succession and rela- 

 tion the reader is referred to that discussion in part I [see p. 29. 

 et. seq.]. 



Structural features 



Except the most westerly part of the region, that occupied by the 

 Upper Devonic strata, all formations are compressed into folds. 

 Many of the smaller folds, especially those in the Catskill district, 

 are still complete. The easy subdivision of strata possible in this 

 district also simplifies the problem of detecting small changes of 

 altitude. But for the most part the larger folds have been beveled 

 off extensively by surface erosion so that only the truncated limbs 



