LETTER OF TRANSMITTAL. 
Department of the Interior, 
United States Geological Survey, 
Washington, D. C. , February 11, 190 1+. 
Sir: I have the honor to transmit herewith manuscript for a new 
edition of Analyses of Rocks from the Laboratory of the United States 
Geological Survey. During the four years which have elapsed since 
the last edition (Bulletin No. 168) was printed, over 1,000 analyses 
have been made, of which nearly 300 are here included. The high 
standard of analytical work which has always prevailed in this labo- 
ratory has not only been maintained but has been sensibly raised. In 
this edition the names are stated which the rocks would bear in the 
classification proposed in 1903 by Messrs. Cross, Iddings, Pirsson, and 
Washington, and set forth by Doctor Wasington in Professional Paper 
No. 14. Mr. Clarke has also given a new computation of the average 
composition of rocks, closely agreeing with his former estimates, but 
founded upon more extensive data. 
Very respectfully, 
George F. Becker, 
-Geologist in charge, 
Division of Chemical and Physical Research. 
Hon. Charles D. Walcott, 
Director United States Geological Survey. 
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