258 
IOWA ACADEMY OF SCIENCES. 
NOTE ON THE CARBONIFEROUS FAUNAS OF MIS- 
SISSIPPI VALLEY IN THE ROCKY 
MOUNTAIN REGION. 
BY CHARLES R. KEYES. 
Recent critical and extensive comparative studies of 
the Carboniferous faunas of the Rocky mountain region 
have disclosed some facts that are of great interest to 
those who have become familiar w 7 ith the Paleozoic fossils 
of the Mississippi valley. The Carboniferous faunas of the 
Continental Interior have now been well understood for 
over half a century. The faunas of the same geological 
age from the vast region west of the great central valley 
of the continent have also been well made out, but for 
the most part by a group of paleontologists entirely dif- 
ferent from that group which was most familiar with the 
fossils of the Mississippi valley. On this account, chiefly, 
the faunas of the two regions have been treated largely 
independently and few exact correlative comparisons made. 
Only in a very general way, in the past, have careful 
correlations been attempted. The results of the recent 
work are therefore of great significance. 
The Rocky mountains abruptly terminate southward 
soon after crossing the Colorado line. Beyond begins the 
Mexican tableland with its characteristic basin-range 
structure. In this part of the southwest the Carboniferous 
is composed chiefly of a lower calcareous portion and an 
upper clayey part. The first-named consists of a number 
of limestone members which attain a thickness of more 
than 2,000 feet; and represent the Lower Carboniferous 
limestone, such as is found at Burlington, Iowa, and the 
limestones of the Upper Coal Measures. No shales of 
importance nor any beds corresponding to the Lower Coal 
