LETTER OF TRANSMITTAL. 



Philadelphia, January 1, 1879. 



Dear Sir : On several occasions you have expressed a desire, that, in 

 my trips to the Western Territories, I should undertake the investigation of 

 the microscopic forms of life which inhabit the waters. During the last 

 four years I have studied one important class — the Rhizopods, as they occur 

 in all fresh waters of the country, from the Atlantic border to an altitude 

 of 10,000 feet in the Rocky Mountains. The marine forms of Rhizopods, 

 in all times, have extensively contributed to the construction of stratified 

 rocks The determination of the living fresh-water forms may serve as a 

 guide to the discovery and determination of fossil forms in the vast lacus- 

 trine formations in the interior of our continent. Herewith, I transmit my 

 report for examination and publication, trusting it may meet with your 

 approbation. 



Respectfully, 



JOSEPH LEIDY. 

 Dr. F. V. Hayden, 



U. S. Geologist, Washington, D. C. 



