302 A. Wandhe — Study of Cape Neddick Gabbro. 



resorbs the magnetite. The essential minerals of the 

 light phase are labradorite, biotite, pyroxene, magnetite 

 and hornblende, the dark minerals being accessory to the 

 feldspar with biotite the most abundant ferromagnesian 

 mineral. The striking feature of the thin sections of 

 these rock types is the anhedral fragment-like habit of the 

 silicate minerals. It is as though movement had taken 

 place in this mass just before final complete solidifica- 

 tion was accomplished. It is possible, therefore, that in 

 the later stages of crystallization of this stock differen- 

 tiation took place largely by the settling of crystals 4 

 the tendency being perhaps for the ferromagnesian and 

 metallic minerals to sink leaving in the upper portion of 

 the stock an accumulation of crystals consisting for the 

 most part of feldspar. Just before complete consolida- 

 tion was effected movement in this crystal mush may 

 have taken place, the relationships as now seen being the 

 result. 



Secondary alteration. — Eecent road-cuts on the Cape 

 made available fresh specimens of the various rock 

 phases that to the eye appear unaltered. The micro- 

 scope, however, shows that the plagioclase, biotite, and 

 olivine have undergone slight alteration. The plagio- 

 clase alters to sericite and calcite, the biotite to chlorite 

 and calcite, the olivine to serpentine. Kaolinization of 

 the feldspar cannot be detected nor is limonite a product 

 of the alteration affecting either the biotite or the olivine. 

 The changes are, therefore, ascribed to post consolida- 

 tion solutions of the general nature of those which 

 usually accompany the ores of mineral deposits. The 

 slight amount of change produced in the rock minerals 

 would indicate that post consolidation hypogene solutions 

 were but sparingly present. 



Contact actions. — The shearing and mashing of the 

 enclosing sediments have already been described. The 

 contact metamorphism of the quartzites is also well 

 shown. Away from any intrusive the quartzites are 

 seen to consist of quartz, with minor amounts of calcite, 

 biotite, chlorite, plagioclase, orthoclase, and rutile. Two 

 suites of specimens were studied from the contact zone, 

 the one consisting of three specimens taken one-hundred- 



4 N. L. Bowen, Journal of Geology, vol. 27, No. 6, 1919. 



