GEOLOGY OF THE LUZERNE QUADRANGLE 21 



same age, but rather that we are deaUng with a great mass of rock 

 which, in a molten condition, was very irregularly intruded into the 

 earth's crust, so that portions of the magma which were partially or 

 wholly solidified relatively early were intruded by more or less still 

 molten material. Much of the magma varied notably in compo- 

 sition on account of differentiation, and considerable portions more 

 or less injected, digested or even assimilated country rock. It 

 should be clearly understood that the M^riter does not now main- 

 tain, nor has he ever stated, that there may not be two granites of 

 distinct^ different ages, for example, Archeozoic (" Laurentian ") 

 and Proterozoic ("Algoman"). What he does mean is that the 

 burden of proof is upon anyone who argues for the two granites. 

 Even if one granite or syenite will ever be satisfactorily proved to 

 be much older than another, it is the writer's opinion, based upon 

 fourteen seasons of field work in the Adirondacks, that any really 

 accurate separation of the two on geologic maps would probably 

 never be feasible. 



Ailing, in his description of the old graphite mine near Conkling- 

 ville,^" indicates the presence of Algoman granite well below the 

 surface in a structure section, but since such rock is nowhere 

 exposed in that vicinity there is, in the writer's opinion, no real 

 warrant for assuming its presence. 



That the rocks of the syenite-granite series have been intruded 

 into, and are, therefore, younger than the Grenville stratified series 

 is a well-established fact. The proof is at least threefold: (i) 

 dikes of syenite or granite and granite-pegmatite cutting the Gren- 

 ville; (2) distinct inclusions of the Grenville in the syenite-granite; 

 and (3) injection, digestion and possibly even assimilation of por- 

 tions of the Grenville by the syenite or granite, especially the latter. 

 Dikes cutting Grenville of the Luzerne quadrangle have been men- 

 tioned in the above description of the Grenville rocks. Inclusions 

 of the Grenville in the syenite-granite are very common, especially 

 in some of the areas of mixed rocks described hereafter. The very 

 small masses of pure Grenville separately mapped are in reality only 

 inclusions in the syenite-granite. In fact the once widespread 

 Grenville was so cut to pieces and displaced by the syenite-granite 

 magma that only the merest remnants now remain within the quad- 

 rangle. Intimate injection of Grenville by granite is abundantly 

 represented in the areas hereafter described as Grenville-granite 

 mixed rocks. 



"N. Y. State Mus. Bui. 199, 191 7, p. 95. 



