40 NEW YORK STATE MUSEUM 



where they are usually amphibolitic. The members of the syenite- 

 granite series are mostly distinctly gneissoid, though at times they 

 are only very faintly so. A striking feature is the frequent rapid 

 change within a few rods from rocks which are very clearly 

 gneissoid to others in which foliation is scarcely visible. The 

 Grenville strata, as usual in the Adirondacks, always show perfect 

 parallehsm of stratification and fohation, these rocks invariably- 

 being thoroughly crystalline. 



Of the many strike and dip observations made in the field, the 

 better ones, so distributed as to show the principal variations, have 

 been selected and plotted on the accompanying geologic map. In a 

 general way nearly east-west strikes greatly prevail, with southerly 

 dips most common in the north and northerly dips most common 

 in the south. To be more exact, the northwestern half of the 

 quadrangle, or all lying north of a line passing from the northern 

 base of Blue ridge to the eastern base of Fishing Brook mountain, 

 shows very few exceptions to a nearly east-west strike and southerly 

 dip, the amount of the dip generally being from 60 to 80 degrees ; 

 while the southern half of the quadrangle, or all south of the line 

 above indicated, exhibits more variations but with an average 

 nearly east-west strike and prevailing northerly dip generally from 

 25 to 50 degrees. 



A noteworthy feature' is the occasional local occurrence of strikes 

 making high angles with the general trend of the foliation of the 

 quadrangle. An example of this in syenite is in the mountain mass 

 lying just east of Tirrell pond (see map). Such a sharp change 

 in strike is more in harmony with the idea that the foliation of 

 the syenite and granite was produced as a kind of flow structure 

 during the process of intrusion rather than by a great force of 

 compression because, if due wholly or even largely to compression, 

 the foliated structure must everywhere have developed essentially 

 at right angles to the direction of the compressive force. 



Exceptional strikes are of most common occurrence in the Gren- 

 ville limestones and in the mixed gneisses, these being readily 

 explained by the fact that such rock masses were most subject to 

 being twisted and disturbed at the time of the great igneous 

 intrusions. 



A most interesting arrangement of strikes and dips occurs along 

 the southern side of the quadrangle within a strip 2 or 3 miles wide. 

 Thus, within the eastern portion of this strip the strikes are mostly 

 northwest-southeast, wath dips to the northeast; toward the middle 



