REPORT OP THE DIRECTOR AND STATE GEOLOGIST 1901 1'29 



near, the floor of a former Triassic area north of the Highlands 

 of the Hudson. Such a view of the origin of the Hudson valley 

 north of the Highlands is borne out by the evident structure of 

 the valley south of the Archaean ridge, and is not incompatible 

 with the structure of the Hudson and other terranes to the 

 north. 



A final reason for the reference of the rock to the Trias is its 

 near-surface character. The field occurrence as described by 

 Professor Woodworth, and the character of the rock, both mega- 

 scopic and microscopic, indicate surface volcanic action. Now, 

 while surface lavas are abundant in the Trias traps, we know 

 of no such among the eruptives of the Champlain valley, the 

 basic rocks there all being in the dike form. To be sure, the 

 rocks of the latter cooled at no great depth below the surface 

 and may have outflowed there, but no vestige of such rocks now 

 remains. 



In conclusion, the only known New York igneous rocks to 

 which the Northumberland rock can be referred, are those of the 

 Champlain valley, and the diabases of the Newark series. 

 Because it is a diabase, and a volcanic, rather than an intrusive 

 rock, the latter reference is regarded as the more probable. But 

 it must be reiterated, at the risk of becoming wearisome, that 

 the evidence is far from decisive, and that this view is pro- 

 mulgated as a working hypothesis simply. 



