THE ADIRONDACK GRAPHITE DEPOSITS 99 



Cushing is, in all probability, the Hague gneiss, somewhat more 

 biotitic than is customary. Above the Faxon is the expected Swede 

 Pond quartzite which " is mere or less involved with the white, 

 garnet-bearing granite which we regard as Laurentian." 1 This is 

 the familiar syntectic Swede Pond gneiss. On climbing the hill 

 this syntectic rock was observed to be penetrated by pegmatitic 

 dikes suggesting the near presence of the Algoman granite. Thus, 

 when the higher slopes and the summit were reached, it was not 

 surprising to find a splendid display of the granite. This was dark 

 grey-green in color suggesting the angite-syenite of the central 

 Adirondacks. The microscope, however, shows the quartz content 

 to be' about 30 per cent, placing the rock among the granites. The 

 ferromagnesian minerals are all altered to serpentine and chlorite, 

 but probably were originally amphiboles. 



The significant fact for us is that this is the Algoman and not 

 the Laurentian granite. The latter rock was injected into the 

 Grenville before that series was folded, and thus it frequently 

 behaves like a stratigraphic unit, not interfering with the contin- 

 uance of the ore in depth. On the other hand, the Algoman came 

 in after the intense folding and its habit is to cut through the sed- 

 imentary layers, which include the ore. Thus the writer strongly 

 suspects that the ore does not continue " all the way to China." 

 How much farther down the dip the workings can continue before 

 encountering the main body of the granite is, of course, not known, 

 but a diamond drill would "settle the matter. 



On the summit of the knoll several small patches of the black 

 metagabbro were observed that remind us of the Hooper property. 

 On the farther side of the same hill a large mass of it was found 

 cut by the Algoman but cutting the Laurentian injected Swede 

 Pond gneiss, thus establishing their relative age relations. That all 

 the metagabbro of the Adirondacks is of the same age is certainly 

 not proved. Doctor Cushing says that " there is certainly much 

 (ortho-)amphibolite in the region which is older than the Lauren- 

 tian and is the oldest eruptive present, so far as I know," 2 There 

 seems to be no escape from the fact that this metagabbro, on the 

 property, is younger than the Laurentian granite but older than the 

 Algoman granite. 



Passing over the metagabbro, an outcrop of the Swede Pond 

 gneiss was again found. At one spot a minor fault was suspected 

 by the brecciated condition of the rock. This gneiss is succeeded 



1 Ibid. 



2 Communicated by letter, November 1917. 



