48 



LARAMIE FLORA OF THE DENVER BASIN. 



dinosaur fauna forms a series of successive genera, the ' 

 phyletic relationship of which is determined by the 

 evolutionary development of skeletal parts, and there is no 

 break in this series from its first appearance low down in 

 the Cretaceous to the final disappearance of the entire 

 group in what we propose to call the close of the Cretaceous. 



The invertebriites were submitted to T. W. 

 Stanton, who commented as follows: 



I have recently examined your invertebrates from the 

 Kdmonton and Paskapoo formations of Alberta. Those 

 which you have already sent from the Edmonton beds 

 include several lots of brackish-water shells, withaslighter 

 mixture of marine forms (Lunatia), and several lots of 

 purely fresh-water shells. The brackish-water collections 

 are certainly Cretaceous and consist of species which all 

 occur either in identical or very closely related forms in 

 both the Judith River and in the brackish-water bed 

 which occurs at the top of the Fox Hills and the base of the 

 Lance. 



The fresh-water collections contain no species charac- 

 teristic of either the Judith River or the Lance, and while 

 some of them, like Goniobasis tenuicarinata, occur in the 

 Lance, the general aspect of the fossils is somewhat more 

 suggestive of [Fort Union than of anything earlier. It 

 should be remembered, however, that Whiteaves has re- 

 ported a number of] Fort Union species as occurring in 

 the Belly River beds of Alberta, and it may be that more 

 of these types than we have supposed range down as low 

 as the Judith River. "^ 



The fossil plants were studied by Arthur 

 Hollick and me and pronounced to be of Fort 

 Union age, though a small collection from the 

 lower part of the Edmonton submitted to me 

 at a later date appeared to be of Cretaceous 

 affinity-."" 



As regards the age of the Edmonton, Brown 

 said: 



The Edmonton formation differs greatly in lithologic 

 character from the Fox Hills, which occupies the same 

 relative position in the United States, where it is a sand- 

 stone formation, but I believe it to have been, in part at 

 least, synchronous with the Fox Hills. It may possibly 

 Vje correlated with the Laramie, according to its original 

 definition. 



In a later paragraph he added: 



The strata (Edmonton) are of marine and brackish- 

 water origin and everywhere conformably overlie the 

 marine beds below. The shale series shows an inter- 

 rupted successive sedimentation from purely marine con- 

 ditions at the base, through brackish water during most 

 of the period, with a gradual freshening toward the top. 

 This formation fulfills the original definition of the term 

 Laramie."' 



" The words in brackets, which were omitted from Brown's paper 

 through an error in transcription or in printing, were supplied by Mr. 

 Stanton in a personal communication to me. 



« Knowlton, F. H., Cretaceous-Tertiary boundary in the Roclty 

 Mountain region; Geol. Soc. America Bull., vol. 25, p. 337, 1914. 



«^ Brown was in error on this point, for, according to King's original 

 definition, the Laramie is the "uppermost member of the conformable 

 Cretaceous series above the Fox Hills." 



According to Brown, the Paskapoo forma- 

 tion, as already mentioned, was conformable 

 on the Edmonton, though he thought there 

 was a time interval between them, as shown by 

 the absence of all or nearl}' all of the Lance 

 formation. The Paskapoo, although contain- 

 ing no dinosaurs, has a small mammal fauna, 

 which, he said, "is more varied than that of 

 the Lance and is comparable to it." 



A late word on the correlation of the Edmon- 

 ton with beds in the United .States is spoken liy 

 Eugene StebLngor °* in his paper on, "The 

 Montana group of northwestern Montana." 

 The uppermost member of the Montana group 

 recognized was here called the Horsethief 

 sandstone, which is the equivalent of the Fox 

 Hills as identified by G. M. Dawson in Alberta. 

 Stebinger's conclusion was as follows: 



Above the Horsethief sandstone in the section on Two 

 Medicine River there are light-colored soft clayey and 

 sandy strata, already referred to as of continental origin, 

 that are identical in appearance with the Belly Ri^er and 

 Judith River strata. Although these rocks ai'e younger 

 than Montana in age, the.v deser\e mention here because 

 they seem to complete for a third time a cycle of sedimen- 

 tation proceeding from purely marine to fresh-water or 

 continental conditions. The first of these cycles is from 

 the marine Colorado shale, through Mrgelle sandstone, 

 to the strata of continental origin in the lower part of the 

 Two Medicine formation; the second is from the marine 

 shale of the Claggett, thnjugh the sandstone in its upper 

 part, to strata, also of continental origin, comprising the 

 Judith River formation; and the third is from the marine 

 Bearpaw, through the Horsethief sandstone, to the conti- 

 nental deposits above that sandstone. The relations in 

 each cycle between the continental deposits and the 

 underlying sandstone seein to be identical. The strata 

 are apparently perfectly conformable, and the impression 

 is very strong that the same conditions ruled in each 

 transition from marine to land conditions, or, in other 

 words, the strata above the Horsethief sandstone are 

 physically as closely related to the Bearpaw shale as the 

 Judith River formation is to the Claggett or the Two 

 Medicine formation to the Colorado shale. Now, these 

 strata of continental origin above the Horsethief sandstone 

 constitute the St. Mary River beds of Dawson, which 

 occupy the same position in the geologic column as the 

 Edmonton formation of central Alberta and approxi- 

 mately thai of the Lance formation of Wyoming. 



"LARAMIE" AND LIVINGSTON FORMATIONS IN 

 MONTANA. 



'I'he area in the vicinity of I^ivingston, 

 Mont., and extending thence southward to 

 the northern border of the Yellowstone Na- 

 tional Park and northward around the Crazv 



«8 U. S. Geol. Survey Prof. Paper 90, p. 68, 19U. 



