Stevenson.] 4:00 [June 18, 



British. America southward, with more or less irregularity, into New 

 Mexico, along the eastern and southern borders of the mountains, with 

 an occasional lignitic bed in the interior of the region ; the other reaching 

 barely beyond our northern line into British America, and extending 

 southward to New Mexico, covering a vast area east from the mountains, 

 as well as within the disturbed region and beyond it at the south in New 

 Mexico. 



For a proper understanding of the conditions here, it may be well 

 to give a brief description of the various formations as they are exposed 

 along the east flank of the mountains. 



Silurian sti-ata rest upon the metamorphic schists, and above them come 

 the Carboniferous, the Devonian being absent, or not satisfactorily iden- 

 tified. Frequently overlapping and concealing these formations, there is 

 a very persistent mass of red beds, more or less conglomerate, and con- 

 taining inarls and beds of gypsum. These have been referred to the 

 Triassic, principally, however, because of negative evidence. They 

 are succeeded by shales containing limestone, which frequently yields 

 Jurassic fossils. Upon this last rests the Cretaceous, of which five well- 

 marked divisions have been ascertained in the upper Missouri region. 

 These are, ascending,* 



No. 1. Dakota Group, sandstones, shales, and lignites. 



No. 2. Fort Benton Group, usually argillaceous shales. 



No. 3. Niobrara Group, limestones and calcareous shales. 



No. 4. Fort Pierre Group, shales with nodules of clay -iron stone. 



No. 5. Fox Hills Group, sandstones, more or less calcareous. 

 In Colorado and New Mexico, especially in the latter territory, it is not 

 always possible to make out the groups accurately, and some of those who 

 have worked in that region are satisfied to use the following classifica- 

 tion : 



Lower Cretaceous, equivalent to No. 1. 



Middle Cretaceous, equivalent to Nos. 2, 3, and 4. 



Upper Cretaceous, equivalent to No. 5. 

 The lower Cretaceous yields animal remains at few localities, and these, 

 in many cases, are of such a character as to render its reference to the 

 Cretaceous a somewhat doubtful one. It contains vast numbers of vege- 

 table impressions, strikingly resembling the Miocene flora of Europe. 



The Middle Cretaceous is quite variable in composition, but there are 

 few exposures of the lower portions which will not yield fine collections 

 of animal remains. The ferruginous nodules of the upper part are in- 

 variably fossiliferous. It occasionally contains thin beds of lignite, one 

 having been observed at Sage Creek, Wyoming Territory, by Dr. Hay- 

 den, and a similar one at Canon City, Colorado, by myself. 



The upper boundary line of No. 5, is very indefinite. Indeed it is th® 

 matter in dispute. The rock is sometimes a rusty arenaceous shale but 



*Thi8 succession was elaborated by Mr. Meek and his co-laborer, Dr. Hayden. 



