Philadelphia, Decemher 18, 1873. 

 Sir: I seud herewith a report on the stratigraphical relations and 

 vertebrate paleontology of the formations which represent the Pliocene 

 epoch, as at present understood, in No-rtheastern Colorado. This essay 

 is based upon material collected by myself during a part of the summer 

 of 1873, under the auspices of the Geological Snrvey of the Territories, 

 of which yon are director. Hoping that it will subserve the objects of 

 the survey, I remain, with respect, 



EDWAED D. COPE, 

 , Paleontologist. 



Dr. F. Y. Hayden, 



Director of the U. 8. Geological Survey of the Territories. 



