478 PROCEEDINGS OF BALTIMORE MEETING. 



groundmass was probably a glass, but it is now mostly devitrified by alteration. It 

 contains innumerable minute green augites, shreds of biotite, many magnetite 

 grains to a slight degree chromiferous, not a few very small perofskites, and apa- 

 tite. It was verbally stated at the Baltimore meeting that no perofskite had been 

 detected, but later, when high powers were used, many grains supposed to be 

 opaque proved to be translucent, isotropic and brown. An analysis by Dr H. 

 Stokes, of the United States Geological Survey, gave the following results : 



SiOa 36.80 NaaO 0.17 



TiOa 1.26 PA 0.47 



AlA 4.16 CO2 2.95 



CrA 0.20 SO3 0.06 



FeO 8.33 S 0.95 



MnO 0.13 H2O below 110° 0.51 



MO 0.09 H2O above 110° 6.93 



CaO 8.63 



BaO 0.12 Total 100.22 



SrO tr. Lessors 47 



MgO 25.98 



K^O 2.48 99.75 



Coarsely crystalline inclusions of a syenitic or dioritic composition were also 

 found, which are probably the " accretions " referred to by Vanuxem in 1835. They 

 appear to be inclusions brought up from the underlying Archean crystallines. In 

 comparative observation on some specimens of the dike described by Dr G. H. 

 Williams from Syracuse, and given to the writer five j'^ears ago, undoubted Archean 

 gneiss was detected, corroborating a previous observation of Dr Williams.* The 

 Dewitt dike has many inclusions of shale and of fossiliferous limestone, but in the 

 slides they show no appreciable effects of contact metamorphism. From a number 

 of well records in the neighborhood it was inferred that the dike had come up 

 through about 4,000 feet of Paleozoic strata and an unknown amount of Archean 

 crystalline rocks. 



The paper will be published in full in the Americiin Journal of Science. 



The petrographic section, at 5.30 o'clock p m, adjourned sine die. 



Session of Friday Evening, December 28 



The evening session was held in Levering hall at 7.30 o'clock p ra, and 

 was wholl}^ devoted to the Presidential Address, which was illustrated 

 with lantern views, and entitled : 



RECENT GLACIAL STUDIES IN GREENLAND 

 BY THE PKESIDENT, THOMAS C. CHAMBERLIN 



The address of the President is printed as pages 199-220 of this vol- 

 ume. 



* Bull Geol. Soc. Am., vol. 1, 1889, p. 533. 



