74 The American Geologist. Feb. isoo 
the extremes both in Arkansas and in Indian Territory, is 
about 10° south of west — a fact which has considerable bearing 
upon the subsequent topographic development of the region- 
The importance of this mountain system and its relation to 
the climate, the structure and the cultural conditions of the 
Southwest have never been defined. It is the presence of this 
elevated barrier in Arkansas that protects the sub-tropical 
Louisiana region from the cold "northers" which blow through 
the central gaps and lowlands of equal latitude in Texas mak- 
ing that state so much colder. It is this mountain barrier 
that condenses the moisture from the gulf of Mexico and pre- 
cipitates in the southwestern Arkansas region fifty inches of 
rainfall annually, while along its almost destroyed central 
course the country is nearly arid. To these mountains are 
attributable the wildness of the country of western Arkansas 
and central Indian Territory, which are perhaps still the most 
impenetrable fastnesses of our country. The present bearing 
of these mountains upon the Texas region, however, is incon- 
spicuous in comparison Avith the grand part they have played 
in the past ; for from all the evidence it is apparent that the 
present elevations of this system are merely remnants of an 
ancient and once magnificent system between the Appalachian 
and Rocky mountain systems, as the Uintas now connect the 
Rockies and the Wasatch. They were elevated after the close 
of the Carboniferous, as shown in the almost vertical fold of 
the rocks of that period which compose by far their greater 
portion. It is also probable that this elevation was prior to the 
deposition of that little studied series of early Mesozoic rocks 
spoken of in this paper as the Red beds, for which Dr. Hitch- 
cock long since applied the name of the "Red Clay formation." 
More evidence is needed to elucidate this point however. That 
the greater portion of the system remained dry land during 
the Lower Cretaceous, the Upper Cretaceous, the Tertiary and 
the Quaternary epochs of subsidence is also evident from the 
absolute non-conformity with which the sediments of those 
periods are laid down against them. There were gaps, how- 
ever, even in Lower Cretaceous time, when these earlier seas 
washed through these mountains and deposited their sedi- 
ments as far north as Kansas, sediments that underlie most of 
the great plains of Texas (except the Staked Plains and the 
Coast Prairies) such as the Grand, the Black the Eo-Lignitic 
