220 



SCIENCE 



[N. S. Vol. XXXII. No. 815 



build a system of generalizations upon the prop- 

 erties of individuals which differ from their neigh- 

 bors in any direction only in degree. 



Discussed by A. C. Gill, Whitman Cross and the 

 author. 



Origin of the Alkaline Rocks: Reginald A. Daly, 



Boston, Mass. 



Most alkaline-rook bodies are associated with 

 subalkaline (lime-alkali) types. The magmas 

 from which alkaline rocks have originated have 

 usually been erupted through limestones or other 

 carbonate-bearing sediments. The thesis was then 

 presented that the majority of the alkaline rocks 

 have been derived from subalkaline (generally 

 basaltic) magma through the absorption of lime- 

 stone or dolomite by the magma. The solution of 

 a relatively small proportion of the carbonate 

 disturbs the chemical equilibrium of the subalka- 

 line magma and its alkalies are concentrated in 

 (generally the upper) part of the magma-chamber. 

 According to conditions the concentration of the 

 alkalies will vary in amount. The hypothesis 

 explains the field associations, and the mineralog- 

 ical and chemical compositions of most alkaline 

 rocks. 



Discussed by J. F. Kemp, Whitman Cross, H. 

 P. Gushing, A. E. Barlow, W. G. Miller and the 

 author. 



The Complex of Alkaline Igneoiis Rocks at Cut- 

 tingsville, Vermont: J. W. Eggleston, Cam- 

 bridge, Mass. (Introduced by J. E. Wolff.) 

 This is an oval area of alkaline igneous rocks, 

 stock-like, with roughly concentric arrangement, 

 and intrusive into gneisses. Syenite, with nephe- 

 line-bearing varieties is the chief type. There is 

 also much essexite. The mass is cut by numerous 

 dikes, including tinguaite and camptonite. In 

 chemical character the rocks are closely related 

 to those of southern Norway, described by Brogger. 

 Discussed by J. E. WolfT, F. E. Wright and J. 

 A. Dresser. 



Obsidian from Brafntimiuhryggur, Iceland: Feed 



E. Weight, Washington, D. C. 



The paper described (a) peculiarly pitted sur- 

 faces on specimens of obsidian which resemble in 

 a remarkable degree the markings of the Austrian 

 moldavites; (6) also a unique type of crystalliza- 

 tion in cavities in this obsidian. 



Bleaching of Granite at Limestone Contacts: H. 



P. CusHiJsro, Cleveland, 0. 



In the Thousand Island region the red granite 

 gneiss of Laurentian age invariably becomes white 

 at limestone contacts and all the granitic dikes 



in the Grenville limestone are white. The color 

 change does not take place, however, at the con- 

 tacts with other Grenville sediments, either 

 schists or quartzites, and the dikes in these rocks 

 are red. Both the cause of the color change and 

 the influence of the limestone in producing it are 

 uncertain. 



Pegmatite in the Granite of Quincy, Mass.: C. H. 

 Wabben and C. Palache, Boston and Cam- 

 bridge, Mass. 



Only two important occurrences of pegmatite 

 are known in the riebeckite granite of Quincy. 

 These are exposed in two of the quarries and take 

 the form of rudely cylindrical masses of consid- 

 erable size entirely enclosed in the granite. In 

 mineral composition they are closely similar to 

 the granite, the essential minerals being quartz, 

 alkali-feldspar, riebeckite and aegirine-augite; ac- 

 cessory minerals so far identified are fluorite, 

 parisite, ootahedrite, ilmenite, wulfenite and the 

 sulphides molybdenite, galena, sphalerite and 

 chaloopyrite. The pegmatites exhibit a certain 

 sj'mmetry of structure. Fine graphic-granite 

 forms a marginal band, succeeded centrally by a 

 zone of coarse granitic texture made up of quartz, 

 feldspar, riebeckite and tegirine-augite. As a rule 

 this zone graduates centrally into almost pure 

 massive quartz, sometimes containing sulphides. 

 In one portion of the largest mass the center is 

 miarolitic and in the cavities thus formed the 

 quartz, feldspar and ipgirine-augite are well crys- 

 tallized, while the rare minerals, noted above, find 

 their principal development. Angular fragments 

 of the pegmatite enclosed in felted crocidolite and 

 deeply corroded crystals of riebeckite partly re- 

 placed by fluorite, point to a final stage of crush- 

 ing and pneumatolytic action. The paper de- 

 scribed these deposits and the minerals in detail. 

 Remarks were made by J. F. Kemp. 



Fayalite in the Granite of Rockport, Mass.: 

 Chaeles Palache, Cambridge, Mass. 

 A recent discovery of large crystals of fayalite 

 in a granite pegmatite near Rockport furnishes 

 for the first time opportunity for an accurate 

 description of this interesting mineral occurrence, 

 the mineral having been twice before foimd here, 

 but in neither case studied in place. 



Microscopic Study of Certain Coals in Relation 

 to the Sapropelic Eypothesis: E. C. Jeffeet, 

 Cambridge, Mass. (Introduced by David 

 White.) 

 Discussed the ingredient matter and relation 



of the same to formation of cannels, kerosene 



