344 T. AV. STANTON CRETACEOUS-TERTIARY BOUNDARY 



iug the Colorado epoch covered a large part if not the whole of the prov- 

 ince, and by the end of the Cretaceous it had entirely retreated from the 

 area; but the Eocene Sea did not return into this province at all. In- 

 stead of marine deposits great continental deposits were formed, begin- 

 ning in the Cretaceous and continuing with many interruptions and 

 witli increasing restriction of areas througliout Tertiary time. In the 

 early days of geological exploration of the Kocky Mountains and Great 

 Plains many geologists believed that all these continental deposits are 

 Tertiary; but with greater knowledge of the history of the region that 

 idea was. long ago abandoned, and many of the continental formations 

 have been recognized as of Cretaceous age, especially those that were 

 subsequently covered by marine Cretaceous sediments. 



EVIDENCE OF LAND AREAS IN THE ROCKY MOUNTAIN REGION 



A brief consideration of some facts in the history of the province dur- 

 ing later Cretaceous time will aid in the correct interpretation of events 

 nearer the close of the period. On another occasion^ I have pointed out 

 some of the variations in the sedimentary record which clearly show that 

 conditions were not uniform throughout the region. The idea has some- 

 times been expressed that this was a period of quiet and universal sub- 

 mergence for the province with no land-masses within it until the end of 

 the period when the whole area was lifted above sealevel by a single move- 

 ment. There are many facts opposed to this view — so many that they 

 form convincing evidence that at several times during the period there 

 were differential movements which brought previously submerged local 

 areais above sealevel. The greatest extension of the sea and presumably 

 the deepest submergence seems to have been near or after the middle of 

 the Colorado epoch ; but even at that time it is probable that there were 

 large islands. The local variations in thickness and character of the sedi- 

 ments bespeak the nearness of land at some localities. 



No argument is needed in support of the statement that a coarse con- 

 glomerate among marine sediments generally means the proximity of 

 land or that coal beds were formed above sealevel, especially when they 

 are accompanied by strata full of the well preserved foliage of land plants 

 or with an abundant fresh-water fauna. By these and other criteria it 

 can be shown that in many parts of the l^ocky Mountain region there 

 were uplifts which made land of parts of the Cretaceous' area in both the 

 Colorado and Montana epochs, and that these movements were not suffi- 



« Timothy W. Stanton: Some variations in T'pper Cretaceous stratigraphy. Jour. 

 Washington Acad. Sci.. vol. .•?. lOiri. pp. .^5-70. 



