HISTORICAL REVIEW OF THE LARAMIE PROBLEM. 



61 



Bowen wrote as follows concerning this 

 section : 



Above the highest marine formation — the Lewis shale — 

 is a mass of continental deposits, divisible into four forma- 

 tions having a maximum thickness of more than 20,000 

 feet. For the lowest of these formations the name Medi- 

 cine Bow is here proposed, because the formation is best 

 exposed and most easily studied' along both sides of North 

 Platte River at the mouth of the Medicine Bow. The 

 Medicine Bow formation is the equivalent of the "Lower 

 Laramie " as defined by Veatch. The latter term is not 

 applicable, for the "Upper Laramie," in the sense in 

 which that term was originally used, is not of Laramie age. 

 As the relation of the Medicine Bow formation to the 

 Laramie of the Denver Basin can not be determined by 

 field relations, and as paleontologists- are not agreed as to 

 the relation of the fossil remains found in the two forma- 

 tions, the use of the unqualified term "Laramie" is not 

 advisable, and it is thought that confusion may be avoided 

 by the use of an entirely new name for the formation 

 hitherto called " Lower Laramie." 



The Medicine Bow formation rests conformably on the 

 Lewis shale and consists of an alternating succession of 

 shale and massive to thin-bedded, ripple-marked, and 

 cross-bedded sandstones, with several beds of coal in the 

 lower third of the formation. * * * 



The Medicine Bow formation is terminated above by a 

 conglomeratic zone taken as the base of the Ferris forma- 

 tion, so named because it is best exposed at' the old Ferris 

 ranch, on North Platte River. * * * As defined the 

 Ferris formation is approximately equivalent to the lower 

 half of -the "Upper Laramie" of Veatch. The conglom- 

 erate at the base of the Ferris formation ranges through an 

 interval of about 1,000 feet, in which massive sandstone, 

 more or less conglomeratic, alternates with nonconglom- 

 eratic sandstone and shale. * * * For the upper part 

 of the "Upper Laramie" as defined by Veatch the name 

 Hanna formation is proposed, because the formation is 

 well exposed to the west and north of the town of Hanna 

 and yields all the coal mined at that place. 



According to Bowen, perhaps the most inter- 

 esting structural problem in the field relates 

 to the occurrence and magnitude of the uncon- 

 formities. He said: 



There are certainly two and possibly three uncon- 

 formities present. The highest of these is at the base of 

 the North Park formation, which overlaps all other forma- 

 tions in the field. 



The next lower unconformity is that at the base of the 

 Hanna formation, formerly assigned to the base of the 

 Ferris formation. It represents the removal of more 

 rather than less than the 20,000 feet assigned by Veatch. 



This was thought by Bowen to be the uncon- 

 formity assigned by Veatch to the base of his 

 " Upper Laramie." Veatch's mistake was per- 

 haps natural, as it resulted from rapid recon- 

 naissance work. 



85344—22 5 



The possibility of a third unconformity— 

 namely, at the base of the Ferris formation- 

 was discussed at length by Bowen, who 

 showed that there is a well-marked conglom- 

 erate at the base of the Ferris formation and 

 in seeking to interpret its significance com- 

 mented as follows: 



The field relations of the Ferris conglomerate and the 

 underlying formation show (1) that the two have been 

 equally deformed; (2) that there is no angular discordance 

 between them either in the Hanna Basin or in other areas 

 where both are present; (3) that the Ferris formation is 

 nowhere known to transgress the Medicine Bow formation 

 and overlap older rocks; (4) that, as previously indicated, 

 the conglomerate seems to have been derived from the 

 same source as the Medicine Bow; (5) that there appears 

 to be a gradual transition from the Medicine Bow formation 

 to the Ferris formation. 



Bowen therefore concluded 



that the weight of e\idence so far as it can now be inter- 

 preted is opposed to the existence of a great unconformity 

 at the base of the Ferris formation, but it is freely admitted 

 that more detailed field work over wider areas is necessary 

 to decide this question. 



As regards the paleontologic evidence af- 

 forded bywhat is now called the Medicine Bow 

 formation Bowen wrote as follows : 



The plants are regarded by F. H. Knowlton as of the 

 same age as the plants of the Laramie of the Denver 

 Basin. The invertebrates are considered by T. W. 

 Stanton as belonging to the fauna of the Lance formation. 

 The bones belong in part to the ceratopsians, but no 

 specimens have been found that are sufficiently diagnostic 

 for even generic determination. 



BLACK BTTTTES, WYOMING. 



Hardly any other locality that is involved 

 in the Laramie problem has given rise to more 

 extended discussions than Black Buttes, Wyo. 

 Being on the line of the first completed trans- 

 continental railway, it was early made easily 

 accessible and, moreover, it happened to fall 

 within the areas studied by three of the geo- 

 logical survey organizations • that worked in 

 the West 40 years or more ago, with the result 

 that it has been discussed and described more 

 frequently and by a greater number of stu- 

 dents than any other similar area that has 

 been referred to the Laramie. The first 

 dinosaur (Agathaumas sylvesLris) accredited to 

 the Laramie, which was supposed to fix the 

 Cretaceous age of everything associated with it, 

 was found at Black Buttes. This locality has 

 also afforded large collections of fossil plants 



