GEOLOGY OF THE BROADALBIN QUADRANGLE 57 



district, as well as the whole Adirondack region, covered by ocean 

 water. We know this because the most ancient formation, the 

 Grenville, is sedimentary in origin and is abundantly represented, 

 not only within the map limits, but also throughout the Adirondacks 

 and in Canada. We have every reason to believe that the Grenville 

 sediments were sandstones, shales and limestones of the ordinary 

 kinds. Judging by the great but unknown thickness of the forma- 

 tion we are led to the conclusion that the oceanic conditions per- 

 sisted for a great length of time which must be measured by hun- 

 dreds of thousands, if not some millions, of years. The Grenville 

 belongs to the most ancient rock group in New York State, or, so 

 far as we know, in the world and, though any attempt to fix its age 

 in years must be very general, it is certain that many millions of 

 years have passed since its formation. The still more ancient land 

 mass from which these sediments were derived and the very ancient 

 ocean bottom upon which they were deposited have as yet not been 

 recognized. That life of some kind was fairly abundant in the 

 Grenville ocean is proved by the presence of graphite which is of 

 organic origin. 



After the Grenville sediments were deposited the whole Adiron- 

 dack region, including the Broadalbin quadrangle, was elevated 

 some thousands of feet above sea level. Tremendous masses of 

 molten rock were intruded into the Grenville just before, during 

 or after the uplift. It is highly probable that the intrusion occurred 

 during the uplift because the force of elevation might also well have 

 pushed the molten masses upward. These igneous rocks are repre- 

 sented within the quadrangle by the syenite and granite. In some 

 cases the Grenville was left practically intact as, for example, the 

 large area on the eastern side of the map ; while in other cases it 

 became more or less involved with the molten flood to give rise to 

 a series of varied rocks as illustrated by the Grenville-Syenite areas 

 on the map. 



After this igneous activity all of the rocks were severely meta- 

 morphosed or changed from their original character by being com- 

 pressed, folded and converted into gneisses. Thus we explain the 

 gneissic or banded structure of all the rocks and the complete 

 crystallization of the sediments. 



Immediately after the great elevation above referred to, the 

 whole land mass began to be eroded and this period of erosion ex- 

 tended over an immense length of time when rock materials of 

 thousands of feet in thickness were removed. This we know be- 

 cause the folded and gneissic structures now at the surface must 



