A Sfinli) of the Belviderc Beds. — ('nKjiii. 365 
Not the diseoveiy of a dicotyledonous tiora in the Chey- 
enne sandstone, but the discovery that this tiora, so far as at 
present known, is of Dakota attlnities, indicates that the Chey- 
enne sediments probably belong to an e]ioeli later than the 
Paluxy. 
But when the Paluxy flora sliall lieconie well known, if it 
prove that it contains no dicotyledons, it must be borne in 
mind that the absence of the latter may be due to ditferences 
of physico-geographic conditions. Wiiile earl}- Cretaceous 
climates were doubtless milder and more uniform than those 
of recent times, there must have been a dei/ree of such climatal 
diti'ei'entiation as now obtains. The lielcldere sea, as we may 
call that portion of the older Cretaceous ocean north of the 
Ouachita mountain-system, was more or less cut off fron) the 
great Texi-Cordilleran ocean that stretched from the southern 
shore of Ouachita land across Texas, Mexico and a large part 
of the Cordilleran region of South America. It was, there- 
fore, perhaps not traA'ersed by warm currents from that ocean. 
And while, in Cheyenne times, the warm temjierate flora of the- 
coming Dakota had already assumed its main features under 
the developmental intiuences of the moderate winter and sum- 
mer seasons that had long prevailed on the great Xebraskan. 
continent of northern Kansas, Nebraska, etc., that tiora may 
have been effectively cut oft' by the Belvidere sea from the 
flora of Ouachita land, and Ouachita land itself, under the 
climatic influences of warm currents from the tropical region 
of the Texi-Cordilleran ocean, nuiy have been occupied by a 
strictl}^ tropical flora that included no dicotyledons. 
Differences of phj'sico-geographic conditions would, on 
general grounds, appear less probable than dift'erences of time 
as the cause of the absence of remains of dicotyledons from 
the Paluxy sands and their presence in the Cheyenne; but it 
should be noted tiiat a i)hysico-geographic exi)laniit ion is at 
least possible. It seems on the whole, however, prol)able tliat 
dicotyledons will yet be found in the Paluxy; and if they be, 
they will no (l()ul)t indicate whether the (heyenne is approxi- 
mately synchronous with or hiter than the Paluxy, the 
chances being that they will show it to l)e later, and belonging; 
therefore to a division not earlier than tiie Fredericksburg. 
