508 RECORDS 



all directions and inclinations, but their courses are mostly com- 

 prised in the northeast quadrant. A few, which are gathered in 

 partially concentric groups of curved planes, also present their 

 convexity toward the northeast. 



2. Every pegmatite occurrence on the Island, without excep- 

 tion, retains more or less structural evidence of having begun its 

 existence as a vein, segregated from a magma or igneo-agueous 

 emulsion. Even the notable dike near 205th Street, crossing 

 the dolomite, retains the vein structure, perfectly in places and 

 imperfectly throughout. 



3. Contact-phenomena are confined mainly to the earlier 

 alteration along seams, to projection of veinlets rather than in- 

 trusion apophyses, and, at one dolomite intersection, to a thin 

 selvage of phlogopite and tremolite. 



4. The vein-structure, often well preserved, presents distinct 

 lamination, correspondent deposits on the two walls, comb-struc- 

 ture, passage from less to more acid minerals toward the centre, 

 and final concentration of minerals of the rarer elements in as- 

 sociation with the significant matrix, smoky quartz, along len- 

 ticular bands, often near a central suture. 



5. Some of the most prominent features, and those by which 

 the simplicity of the problem has been disguised, are the results 

 of pressure upon the original veins through organic movements 

 of the stratum of schists, viz., Assuring, faulting, crushing, shear- 

 ing with development of mica (aptite), re-fusion and development 

 of new phenocrysts (granite-porphyry), and generation of reaction 

 borders outside of each wall of a vein. When flowage has taken 

 place and some transference of the crushed vein material along 

 the plane of the vein, the appearances of a dike begin. Many 

 of these results may be distinguished along the course of the 

 same vein at intervals of a few yards or rods, but in the most 

 characteristic dikes the vein structure is rarely, if ever, completely 

 obHterated. 



Both of the papers presented were discussed by Professor 

 Martin, Dr. Hovey, and others. 



Theodore G. White, 



Sea^etary. 



