IV LETTEK. 



connected in a similar capacity with Col. W. F. Raynolds, United States 

 Engineers, director of an expedition to tlie Lower Yellowstone, and during 

 this time much additional material of value was obtained. The cordial thanks 

 of the writer are due to these gentlemen for their most important aid and 

 encouragement. 



This memoir will soon be followed by the " Flora of the Lignitic 

 Group" by Leo Lesquereux, containing sixty-five beautifully-engraved quarto 

 plates. 



Very respectfully, your obedient servant, 



F. V. HAYDEX, 



United States Geologist. 

 Hon. Z. Chandler, 



Secretary of the Interior. 



