LEVfER OF TRANSMITTAL 
Department of the Interior, 
United States Geological Survey, 
Baltimore, Md., March 17, 1894. 
Sir: I have the honor of transmitting herewith, for publication as a 
bulletin of the Survey, a paper by Miss Florence Bascom on the 
Ancient Volcanic Eocks of South Mountain, Pennsylvania. 
This work was done in the field during- the summer of 1892 and in 
my laboratory during the winter of 1892-93. That part of it relating 
to the acid eruptive rocks was accepted in June, 1893, as a thesis for 
the degree of doctor of philosophy at the Johns Hopkins University. 
Since that time the paper has been amplified and improved, and I 
believe that the detailed investigations which it describes will prove to 
be of permanent value in elucidating the character and history of 
ancient volcanic rocks, not merely in South Mountain, but in many 
other regions of the Eastern United States. 
Very respectfully, 
George H. Williams, 
Geologist, 
Hon. J. W. Powell, 
Director United States Geological Surveij. 
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