40 NEW YORK STATE MUSEUM 



parallelism. This structure is accentuated by the dark-colored 

 minerals. A rock with such a structure is said to be a gneiss (pro- 

 nounced "nice"). Many ledges of Adirondack syenite or granite 

 exhibit this structure perfectly, but in other cases it is very faint or 

 absent. This phenomenon has generally been ascribed to the flat- 

 tening and fiowage of the minerals under great pressure in the 

 earth's crust after the cooling of the rocks. But very recently the 

 Avriter has presented much evidence in support of the view that the 

 phenomenon really represents a sort of "flow-structure" produced 

 by currents under moderate pressure during the crystalHzation and 

 when the rocks were at least partially molten. The rapid changes 

 in direction and the sweeping curves exhibited by the gneissic struc- 

 ture strongly support the " flow-structure " idea. 



Rocks presenting the characteristics of the syenite and granite are 

 typical plutonic, igneous masses which certainly never reached the 

 surface by intrusion. They were very slowly intruded and slowly 

 cooled under great pressure thousands of feet below the earth's 

 surface. It should be reiterated that rocks of this sort now appear 

 at the surface simply because of vast removal by erosion of the 

 overlying materials. 



That these syenite-granite rocks are younger than the anorthosite 

 has been demonstrated by finding tongues of the former cutting or 

 breaking through the latter (see figure 6) as well shown, for 

 example, a few miles east of Tupper Lake village, and on the 

 eastern face of Whiteface mountain. 



First known uplift of the Adirondacks. We are now ready to 

 discuss the earliest known uplift of the whole Adirondack region 

 above sea level, or, in other words, the birth of the first known 

 Adirondack mountains. As we have learned, the very character 

 and structure of the rocks now exposed to view in the region show 

 conclusively that they were at one time deeply buried, the inference 

 being perfectly plain that those materials have been removed by 

 erosion. Profound erosion of any land mass means that the land 

 must have been well above sea level, and thus we come to the 

 important conclusion that the great mass of rocks, including Gren^ 

 ville etrata, anorthosite and the syenite-granite series, were upraised 

 well above sea level. Just when the uplift occurred can not be 

 positively stated, but there is much evidence favoring the idea that 

 it was concomitant with the great igneous intrusions, especially of 

 the syenite-granite. It is reasonable to believe that the same great 

 force which caused the welling up of so much liquid rock might 

 easily have caused a decided uplift of the whole region. The 



