of Colorado and New Mexico. 527 



tered Tertiary material from the Rocky Mountain region, and 

 for the first time adequately described and figured it ; there was 

 no change in his opinion regarding the stratigraphic position of 

 the Raton Mesa material. 



From 1878 to about 1905, which later date marks the renewal 

 of interest in this field, work on the paleobotany of the Raton 

 Mesa region was desultory and relatively unimportant. About 

 1883 Doctor Newberry obtained and described a few species, 

 also from the upper beds. About the time Newberry wrote, 

 the age of the beds had come to be regarded as Laramie, appar- 

 ently on the mistaken assumption that they were of the same 

 age as the coal-bearing rocks of the Denver Basin which had 

 then come definitely to be known as Laramie. From that time 

 until the work was done that has resulted in the present study, no 

 critical examination was made of the fossil plants, hence this 

 erroneous assumption remained unchallenged. 



In 1907 Mr. W. T. Lee * began a study of the coal in the 

 Raton field, and while prosecuting this work he discovered the 

 presence of an unconformity in the midst of the section of coal- 

 bearing, supposed Laramie rocks. This unconformity was 

 traced throughout the entire Raton Mesa and subsequently was 

 carried around the southern end of the mountains and well up 

 along their west front. f The rocks below the unconformity, 

 to which the name Yermejo formation has been given, have a 

 maximum thickness of only about 375 feet, while the rocks 

 above the unconformity, now called the Raton;); formation, are 

 about 1600 feet in thickness. In some places the Raton for- 

 mation rests on the full thickness of the Yermejo formation, 

 while in other localities the Vermejo is greatly reduced, and in 

 at least one place the entire Yermejo, together with the under- 

 lying Trinidad sandstone, has been removed and the Raton 

 rests directly on Pierre. 



When the unconformity had been demonstrated it became 

 of the greatest interest and importance that the fossil plants 

 should be studied to ascertain their bearing, first on the distinct- 

 ness of these two formations, and second, as to their bearing on 

 the question of age. The present study was undertaken to fur- 

 nish such answers as it might to these two questions. The 

 writer has been fortunate in having at his disposal the original 



*Bull. Geol. Soc. Am., vol. xx, pp. 28-30, 1909. 



fBull. Geol. Soc. Am., vol. xxiii, pp. 571-686, 1912. 



\ Raton formation is the name recently adopted by the U. S. Geological 

 Survey for the coal-bearing rocks above the unconformity in the Raton Mesa 

 region of southern Colorado and northern New Mexico. Those below the 

 unconformity have been named Vermejo formation. The two constitute 

 what has heretofore been called Laramie in this region. The data upon 

 which they were separated are contained in a forthcoming paper on the 

 Raton Mesa region by F. H. Knowlton and W. T. Lee, which will be pub- 

 lished by the U. S. Geological Survey. 



