WARKEN. — ALKALI-GRANITES AND PORPHYRIES. 233 



through the rock are minute black hornblendes averaging not far 

 from a millimeter in cross section. 



Microscopic. — The microscope shows that in the fine-granite of 

 the Ruggles Creek type the minerals present are : — albite-microcline 

 microperthite, quartz and riebeckite with accessory zircon, magnetite 

 and ilmenite, fluorite, a little titanite, calcite, biotite, chlorite and 

 limonite. The last three and a part anyway of the magnetite are 

 secondary, and are present to only a small extent except in the heavily 

 altered surface layer. In the fine-granite of the Pine Tree Brook 

 reservation, we find in addition to the minerals above mentioned, 

 aegirite, a green alkali pyroxene, occasionally small amounts of aenig- 

 matite and rather more abundant fluorite. 



The porphyritic texture noted megascopically is inconspicuous in 

 thin section, for the reason that the feldspars are someAvhat grada- 

 tional in size and the larger grains are relatively so few that tliey are 

 largely lost sight of. While the limits of size of the mineral grains lie 

 between rather narrow limits, the texture of the rock may probably 

 be best described as holocrystalline granular seriate. The feldspars 

 are essentially identical in character and habit with those of the 

 coarse-granite. The quartz is slightly less abundant and shows a 

 tendency to micrographic intergrowth with the feldspar. In fact 

 from some outcrops, probably near to the original contact with the 

 slate, the graphic intergrowths are a prominent feature of the rock. 

 The riebeckite is also essentially the same in habit and optical charac- 

 ters as in the coarse granite. In general it appears that in the fresh 

 rock a green tone predominates over blue (except about the margins) 

 for the ray (a) which is nearest the cleavage. The zircon is usually 

 present in well formed crystals, which is in sharp contrast to the habit 

 of this mineral in the coarse-granite. Aegirite, as has been noted, 

 is present in the fine-granite from the relatively small outcrops on 

 Pine Hill and in the Pine Tree Brook Reservation. Whether it was 

 originally present in the mass northeast of Fox Hill cannot be told, on 

 account of the extreme alteration of the dark minerals, but the general 

 impression is that it was absent. This aegirite has the same relation 

 as those described for the granite. In addition to the aegirite a deep 

 green pyroxene closely resembling aegirite in general appearance but 

 somewhat less pleochroic and of much lower double-refraction and with 

 a larger extinction angle is present. This occurs either in separate, 

 sub- to anhedral grains or is enclosed in the hornblende. It is often 

 strongly altered to ferruginous material. It seems to be essentially 

 the same pyroxene which appears sparingly in the coarse-granite and 



