152 ROLLIN T. CHAM BERLIN 



newly uplifted mountains was deposited nearby and formed the 

 now prominent non-marine Red Beds. Erosion of the mountains 

 continued through the Triassic and part of the Jurassic, approaching 

 peneplanation before the close of the Jurassic and preparing the 

 way for a marine invasion in Upper Jurassic times. ^ The sub- 

 mergence did not last long, and upon the graded plain abandoned 

 by the sea and the peneplaned area surrounding it the streams of 

 early Comanchean time spread out the sediments of the Morrison 

 formation.^ 



The Cretaceous period was a time of very extensive marine 

 sedimentation in the Rocky Mountain region. Lee has brought out 

 the fact that the Dakota sandstone, and probably also the overlying 

 marine Cretaceous formations, formerly extended uninterruptedly 

 over the areas now occupied by the Colorado Rockies.'' These 

 Cretaceous beds mark the last great marine invasion of the interior 

 of North America and are represented by a thick stratigraphic 

 column. In waning Cretaceous times the seas shoaled and with- 

 drew, causing marine sedimentation to give way to terrestrial 

 deposits with included coal beds. 



Laramide diastrophism. — The Cretaceous period was the long 

 quiet before the storm. At its close the growing stresses within 

 the earth sought relief in folding movements. These were of a 

 pulsatory nature, for at least two distinct periods of folding have 

 been distinguished. In northern Colorado the first of these followed 

 the deposition of the Laramie formation of the Denver Basin. But 

 in southern Colorado no folded formation so late as this has been 

 preserved, owing to the greater erosion there in the interval between 

 the folding and the deposition of the basal Eocene. In that 

 region the last formation affected by the Laramide disturbance 

 which has escaped removal is the Vermejo formation of the Mon- 



'^ Ibid., pp. 7-12 and 24-41; also W. N. Logan, "A North American Epicontin- 

 ental Sea of Jurassic Age," Jour. Geol., VIII (1900), 242-73. 



2 See C. C. Mook, "A Study of the Morrison Formation," Ann. New York Acad. 

 Sci.,XXVII(igi6},3i-igi. 



3 Willis T. Lee, "Relation of the Cretaceous Formations to the Rocky Moun- 

 tains in Colorado and New Mexico," U.S. Geol. Survey, Prof. Paper gj-C (1915), 

 pp. 27-58. 



