286 >. p. EMMONS — OROGRAPHIC MOVEMENTS. 



changes in plant life would be produced in t lie progress of geological time 

 than where such movements produced an entire submergence of adjoining 

 land areas. Hence it is to the successive changes in vertebrate life that we 

 must look for the most definite palaeontologies! evidence of the lapse of geo- 

 logical time. 



Palaeontologists tell us that, between the vertebrate fauna of the lowest 

 Eocene beds yel studied in this region and that of the Laramie, there is an 

 important gap in the normal succession of life that remains to be filled. It is 

 now over fifteen years since Mr. King stated from the evidence then available 

 that no Eocene beds' existed on the eastern flanks of the Rocky Mountains, 

 and this statement has held good until within the last year, when an exten- 

 sive series of beds, over 7,000 feet thick, discovered by Mr. R. C. Hills at 

 Huerfano park, on the eastern flanks of the range, have been determined to 

 be in part of Eocene age, though they have not yet been sufficiently studied 

 to determine their entire vertical range in the geological column. These 

 beds overlap the upturned edge of the Laramie beds, as do, or did before 

 removal by erosion, the Arapahoe and Denver beds already alluded to. It 

 is probable that, as special investigations to this end are made, other scries 

 of beds, occupying an intermediate position between the lowest Eocene now 

 known in the region and the coabbearing Laramie, will be discovered; 

 and it may be hoped that in time the gaps in the succession of life may 

 be filled. From the nature of things it will probably be a long time 'ere 

 Buch a complete knowledge of the succession of fauna can be obtained. 

 These later beds were of limited and local extent, they have Kern hut im- 

 perfectly consolidated since their deposition, and, being the first to be affected 

 by Tertiary erosion, they exist now only in fragmentary patches; hence it 

 requires such minute and detailed study to determine their true Btratigraph- 

 ical relations as in the present stage of geological investigation in this coun- 

 try can seldom lie accorded to them. Hence all determination.- of BUCCes- 

 Bion of life based on pahuontologieal evidence alone, must for a long time be 

 provisory. It would seem, therefore, to be illogical, when there is an appar- 

 ent conflict between the definitely determined physical evidence of an oro- 

 graphic movement and that afforded by analogy with the laws of succession 

 established in other parts of the world, to allow the former to he neglected 

 or even to be outweighed in making such provisory determinations. 



