HISTORICAL EEVIEW OF THE LAKAMIE PROBLEM. 



37 



the Colorado epoch m Utah and WA^oming; 

 coal and fresh-water deposits in the Eagle and 

 Judith River formations; and finally, the 

 volcanic activity which furnished material for 

 the Livingston formation in the area ahout the 

 Crazy Mountains in Montana. 



Stanton also devoted several pages to the 

 consideration of the Lance formation, including 

 its distribution and general character, its 

 development in North and South Dakota, and 

 particularh- the marine member and its fauna. 

 Regarding this fauna he said : 



In my opinion, the invertebrates from the marine mem- 

 ber of the Lance belong to a Cretaceous fauna. This is 

 indicated both by their close relationship with the Fox 

 Hills fauna and by the known paleogeographic facts of 

 the late Cretaceous and the Eocene. The fauna contains 

 a ntmiber of species identical with Fox Hills forms, others 

 that are closely related, a few that were ascribed to the 

 Fox Hills but apparently were actually collected by the 

 early explorers from beds now assigned to the marine mem- 

 ber of the Lance, and a considerable nimiber of new 

 species, which, so far as known, do not occur outside of 

 the marine member. * * * The fauna lacks a nimiber 

 of common Fox Hills species and contains a considerable 

 proportion of new forms, so that if may be called a modified 

 Fox Hills fauna. 



The conclusions reached are stated as follows: 



In my opinion, therefore, the conclusion is justified 

 that the Cretaceous period did not end in the interior 

 pro\ince until the sea had completely retreated from the 

 pro\-ince, and that the Lance formation should be assigned 

 to the Cretaceous. 



The final retreat of the Cretaceous sea from the interior 

 proWnce was doubtless associated more or less closely with 

 local erogenic movements which caused active erosion to 

 begin or to increase in various areas; but in other areas 

 within the pro\'ince the products of this erosion were laid 

 down as terrestrial deposits, which taken together practi- 

 cally bridge the gap between Cretaceous and Tertiary. 

 The boundary between the two systems in such areas is 

 not marked by an important break caused by general 

 diastrophism, because the breaks and discordance and 

 erosion intervals in an area of continental deposition are 

 not dependent on the same conditions that cause the 

 major breaks in marine sediments. Even if it be true 

 that there was a world-wide movement at the close of the 

 Cretaceous which caused a break between marine Creta- 

 ceous and marine Eocene in all the areas where such 

 sediments are now accessible, such a movement would 

 not necessarily affect the accumulation of continental 

 deposits of detrital material in an area already above sea 

 level, and in this case apparently it did not affect it. On 

 the other hand, terrestrial deposits are characteristicall)' 

 and necessarily irregular, and the importance of breaks 

 and unconformities in them must therefore be tested with 

 great care, using all kinds of available evidence. 



The Lance formation is believed to be Cretaceous on 

 account of its intimate stratigraphic relation with the un- 

 derlying marine Cretaceous, on account of the close rela- 



tionship of its vertebrate and nonmarine invertebrate 

 faunas with Cretaceous faunas, and on account of the 

 occurrence in one area of a marine Cretaceous fauna within 

 the formation. This marine Cretaceous invertebrate fauna 

 is held to establish the Cretaceous age of the plants which 

 occur in the beds beneath it, in spite of the fact that these 

 plants are said to belong to Eocene species. In other 

 areas where the Lance formation does not include a marine 

 member but has a thicker development of strata, with a 

 large vertebrate fauna of Mesozoic types, it is a fair infer- 

 ence that the whole formation, with its contained flora, is 

 also of Cretaceous age.^ If, then, the Lance flora is in fact 

 a Cretaceous flora, notwithstanding its close relationship 

 with Eocene floras, it is obvious that the correlation of 

 other formations with known Eocene formations on the 

 evidence of fossil plants alone is open to serious question. 

 In the case of the Denver and Arapahoe formations such a 

 correlation is directly opposed by the evidence of the ver- 

 tebrate fauna, which allies them closely with the Lance 

 formation. 



In the contribution of Barnum Brown -* to 

 this symposium he stated that he had been 

 "continuously engaged since June, 1900, in 

 the exploration of the geology, flora, and fauna 

 of three great formations which in their animal 

 and plant life bridge over the passage from 

 Cretaceous to Eocene time, as determined by 

 the comparison with the life of the same epochs 

 in Europe." These formations are "Hell- 

 Creek formation of northern Montana; series 

 embracing in descending order Paskapoo, Ed- 

 monton, Fort Pierre (upper), Belly River (in- 

 tercalation), Fort Pierre flower) of Red Deer 

 River, Alberta; Ojo Alamo formation of north- 

 ern New Mexico; Lance Creek formation of 

 Converse County, Wyo." 



In a former paper Brown had described his 

 "Hell Creek beds" as resting unconformably 

 on the underlying Fox Hills, but this statement 

 he now desired to modify. He described a 

 number of localities in which " these marine 

 beds [Fo.x Hills] have been eroded in places, 

 sometimes to a depth of 10 feet, before the 

 succeeding massive sandstone of the fresh- 

 water 'Lance' was deposited." This break, 

 he concluded, "is evidently of local erosional 

 character," as "the strata are, however, in all 

 cases parallel to the bedding planes of the suc- 

 ceeding sandstones. " 



The Paskapoo and Edmonton formations 

 as exposed along Red Deer River, Alberta, 

 were described at some length. The conclu- 

 sion was reached that the Paskapoo has a 

 mammal fauna in which " the multituberculates 



28 Cretaceous Eocene correlation in New Mexico, Wyoming, Montana. 

 Alberta: Geol. Soc. .\merica Bull., vol. 25, pp. 335-380, 1914. 



