102 NEW YORK STATE MUSEUM 



eclly complicates the underground structure throughout a consider- 

 able belt. , ,• 



6 The Highlands area terminates in a serrate margin which, in 

 the latest thrust movements from the southeast, must have created 

 very unequal distribution of stresses within the slate-limestone 

 region to the north causing additional cross folding and faulting. 

 For the most part these can be traced only a short distance before 

 losing their identity. 



In a mountain folding movement, the uppermost rocks are most 

 broken and displaced or crushed while those of greater depth ma\- 

 be bent or uniformly folded or even recrystallized. It would ap- 

 pear that this latter was the condition of the Highlands rock series 

 during its earlier history. And even in the latest movements its 

 lines appear to be less radically disturbed than the slates and lime- 

 stones to the north. :\Iost of the disturbances that invite serious 

 consideration belong to the latest period of these mountain-making 

 upheavals. 



Comparison of routes 



I New Hamburg group. This group of crossings is in the 

 later sedimentary series. Hudson River slates and Wappinger 

 limestone are the chief formations. But within the southern third 

 of the tunnel, at least, the underlying Cambric quartzite and the 

 older Highland gneiss would be cut — the quartzite possibly three 

 times. The succession therefore will be of considerable complexity 

 as a whole. 



All of the formations involved are thrown into very steep dips 

 at most places and are consequently liable to rapid and unexpected 

 changes — some of which probably do not show at the surface. 



There are several fault lines belonging to the major northeast 

 and southwest series to be crossed by such a tunnel — one of them 

 in each case being met at considerable depth and beneath or adja- 

 cent to the river. These faults besides being the weakest zones of 

 rock as a rule, are in addition the most unstable in any possible 

 future earth movements. Although there is no evidence of recent 

 displacement along these lines, still such a thing is always possible 

 and recent serious effects of this kind on the Pacific coast suggest 

 caution. It is manifestly advisable, if possible, from every stand- 

 point to avoid crossing several of them. 



In the field there are numerous springs of very large flow along 

 many of the limestone borders. The concentration of them to 

 these situations in addition to the occurrence of an occasional sink- 



