CHAPTER II 



ENVIRONMENT OF THE TITANOTHERES AND EFFECT OF ADAPTIVE RADIATION ON THEIR 



VARIATION 



SECTION 1. GEOLOGY AND GEOGRAPHY 



CORRELATION OF EARLY TERTIARY EVENTS IN THE ROCKY 

 MOUNTAIN REGION WITH THOSE IN WESTERN EUROPE 



The recorded history of the titanotheres extends 

 from the upper horizons of the lower Eocene series 

 (upper Ypresian or upper Wind River horizon) 

 through the middle and upper Eocene to the top of 

 the lower Oligocene (Sannoisian or Chadron horizon), 

 covering a period estimated at 450,000 to 600,000 

 years. This estimate is based on the assumption 

 that 9,000 to 12,000 feet of sediment was deposited 

 during the period from basal Eocene to lower Oligocene 



time and that the average rate of deposition was 1 

 foot in every 100 years. 



The Eocene type formations (Wasatch, Bridger, 

 etc.) of the Rocky Mountain region in North America 

 have gradually acquired a time significance, similar 

 to the stages (etages) into which the Eocene and 

 lower Oligocene of Europe are divided, as shown in 

 the following table. The correlation in time between 

 France and America is close for some periods, as, for 

 example, between the Sparnacian and lower Wasatch 

 and between the Sannoisian and Chadron. For 

 other periods the correlation is provisional, because 

 the faunal relations are interrupted. 



Provisional correlation of European and American geologic stages and life zones of the tifanothere epoch 



" The United States Geological Survey classifles the Lance formation as Tertiary (?), the Laramie formation as Upper Cretaceous, and the Denver as Eo 

 author of this monograph believes that the Lance formation is equivalent in part to the Laramie and Denver formations and that it is of Cretaceous age. 



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