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REPORT ON THE PETROGRAPHICAL LABORATORY. 



By Assistant Professor J. Eliot Wolff. 



The instruction in Elementary Petrography was attended by 

 fifteen students. The usual lectures were given twice a week, 

 supplemented by a large amount of laboratory work. Mr. C. L. 

 Whittle was appointed assistant by the Corporation, and gave the 

 instructor much needed aid in the care of the laboratory and the 

 more systematic arrangement of the laboratory work. 



Six students pursued advanced work in Petrography, and made 

 original investigations in the following subjects, among others: — 



The Felsites of the Boston Basin. 



The Schistose Bombs of the Laacher See, in the Hubbard Collection. 



A Basic Dike in the Connecticut Triassic. 



During the winter extensive improvements were made in the 

 geological workshop in the basement, and in the arrangements for 

 illumination and projection in the Petrographical Lecture Room up- 

 stairs, and in the large Geological Lecture Room. The increasing 

 size of the classes and large amount of mechanical work done by 

 them and other students of geology, in slicing and polishing rocks 

 and fossils and preparing thin sections, made the use of power 

 desirable, and almost necessary. A five-horse power electric motor 

 was therefore placed in a corner of the Chemical Laboratory in 

 the basement, and the shafting carried through the wall to the 

 adjoining workshop. From this a lathe is run carrying the ver- 

 tical tin disk charged with bort for sawing rocks, and three other 

 lathes with horizontal revolving iron or zinc plates for grinding 

 and polishing rocks and sections through the different stages. 

 A useful saving of time and labor is thus gained over the old 

 method of working by foot and hand power. 



At the same time a one-kilowatt, 55-volt dynamo is run from 

 the motor by suitable shafting, and the current carried to the two 



