AGE OF THE LIGNITE FORMATION. 

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ton, and below the lowest lignite bed. They were not stray s socinions: 
_— but were brought to light in digging out some of the turtle bones in 
_ the Bad Lands south of Wood Mountain (on the horizon marked by an 
asterisk. Plate VII. Fig. 2.) Dinosaurian bones occurred within a few 
feet of them. 
461. It should be remembered in discussing the age of these pean that 
the fossils of No. 5 have been compared with those of the Mestricht, &c., 
of Europe, the Cretaceous position of which has not at all times been 
undisputed, and should any isolated patches of higher beds than the 
Mestricht and associated formations occur, showing even the strict con- 
tinuance of marine conditions; it is to be doubted whether they would 
be referred to the Cretaceous. Dr. Hayden thus writes of the fifth divi- 
sion of the western Cretaceous :—‘‘ We would also remark that a few of 
the forms found in our Fox Hill beds, particularly the Gasteropoda, 
present such close specific affinities to Tertiary shells, that we would 
_ have doubted the propriety of referring them to the Cretaceous epoch, 
were it not for the fact that we find them associated in the same bed 
with Baculites, Ammonites, Scaphites and other Cretaceous genera and 
species.” 
462. The general bearing of the evidence, in so far as it is now known, 
seems in favour of the Eocene Tertiary age of the western Lignite forma- 
tion, though it may not be exactly synchronous with that of Europe; and 
its base is very probably somewhat lower than that of the formation 
in its typical European localities. Taking into consideration, however, the 
acceleration of the extinction of those pelagic forms, on which our defini- 
tions of the Cretaceous period are largely based, by geographical change 
in the area in question, there would seem to be no impropriety in allow- 
ing a great part of the strata to be called beds of transition. I am also of 
opinion, that further and more complete investigation of these rocks of 
disputed age, instead of indicating more precisely any line between the 
Mesozoic and Cainozoic of the interior region of North America, will 
tend to show the overlap of life forms of different type to be more and 
more complete, and the sequence more perfectly uniform. It will also 
probably be found, over this area, that the rocks of many different localities, 
with more or less distinct organic remains, now considered as representing 
the life of separated periods in a linear succession, may be found by the 
mingling of the fauna and flora in other localities,as the area of study 

* Geological Report Yellowstone and Missouri Expedition, p 26, 

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