STRATIGRAPHIC POSITION OF LANCE FORMATION 375 



unreliable. For instance when a coal-bed that occurred near the 

 top of the so-called somber-colored Lance formation was traced 

 accurately for only a few miles it was found that the position of 

 the dark-colored and the yellow beds varied as much as 300 feet, 

 that is, at one point, the coal-bed might be 150 feet down in the 

 somber-colored portion, and at another, an equal distance up in 

 the yellow beds. It may therefore be confidently stated that the 

 Lance formation and acknowledged Fort Union cannot be sepa- 

 rated formationally on either structural or lithologic grounds, 

 though in general the lower beds are on the whole prevailingly 

 somber in color, while the upper beds are prevailingly yellow. 



MAGNITUDE OF UNCONFORMITY AND BOUNDARY BETWEEN 

 CRETACEOUS AND TERTIARY 



Having demonstrated the existence of unconformable relations 

 between the Lance formation and the underlying formations, the 

 question naturally arises as to the magnitude of this discordance 

 By some it is claimed that it is merely local and is not more impor- 

 tant than other breaks said to occur at various intervals in the 

 Lance formation, and the doubt is expressed whether, even if the 

 unconformity is present, any great amount of erosion is indicated. 



The wide area over which its existence has now been demon- 

 strated certainly removes it from the category of "local" happen- 

 ings, and the uniformity of its occurrence beneath the Lance forma- 

 tion is sufficient indication of its importance over any that have 

 been thus far even apparently indicated within the formation. 

 Now as to its magnitude. It has been shown that in Carbon 

 County, Wyoming, the Lance formation is not only above the full 

 thickness of the "Laramie" (6,000 feet) but is separated from it 

 by an unconformity that Veatch states is fully 20,000 feet, and 

 moreover this unconformity is in the same position as regards the 

 Laramie as that in the Denver Basin of Colorado, which, accord- 

 ing to Cross, has involved the' removal of from 12,000 to 15,000 

 feet of strata between the Laramie and overlying formations. 

 It is possible that the figures given by Cross and Veatch may be 

 too high, but even so, the unconformity is undoubtedly one of 

 importance, and this wOuld seem to dispose of the contention that 



