42 NEW YORK STATE MUSEUM 



Its typical behavior is sill-like (laccolith), often acting like a mem- 

 ber of the Grenville strata in a given case, but frequently it cuts 

 diagonally across the bedding. At the Hooper mine it cuts out the 

 ore at the west end of the property after it has acted as a capping 

 rock for a long distance. 



The rocks above mentioned were folded and faulted before the 

 intrusion of the anorthosite, as well as of the syenite, quartz-syenite, 

 syenite-granite and granite that are different phases of related deep- 

 seated rock masses. These syenite-granite rocks and their dikes 

 (pegmatites) are in the main responsible for the development of 

 the contact type of graphite already treated. In the southern area 

 they have another significance for the miner, and that is in the way 

 they frequently cut the ore. Such considerations are important in 

 estimating ore reserves. 



These rocks are here assumed to be of Algoman age. This corre- 

 lation is merely suggested in the same way that the term Laurentian 

 has been used. 



Following the Algoman granitic rocks in time of intrusion is the 

 long recognized Adirondack gabbro — green-black in color, often 

 showing long, slender needles of feldspar (labradorite) and likewise 

 referred to the Algoman. 



The list of rock units is completed by the trap or diabase dikes, 

 coal-black bands from a few inches to many feet in width, that cut 

 all the above-noted rocks. 



Thus summing up the Adirondack rocks, placing the oldest rocks 

 at the bottom, the geological column would be : 



Keweenawan, in part Diabase 



Gabbro 



Algoman. 



Granite 

 Syenite 

 Anorthosite 



T f Metagabbro 



Laurentian j ° 



Granite 



Grenville series 



Para-schists 



Para-gneisses 



Quartzites 



Para-amphibolites 



Limestones 



