NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 53 



"The eastern area of the Etiid formation is triangular, and occupies several 

 counties in the central part of the Territory, in which there is little hard rock of 

 any kind. Its eastern boundary is approximately along a line from Blackwell to 

 Norman, and its western limit is along a line from Alva to El Reno. It includes east- 

 ern Blaine, Canadian, and Woods Counties, all of Grant, Garfield, and Kingfisher, 

 and the western parts of Kay, Logan, Noble, Oklahoma, and Cleveland Counties. 

 "Throughout this area the soil is red, except where later deposits cover the 

 uplands, or among the sandhills north of some of the streams. Red clays and occa- 

 sional ledges of thin sandstone outcrop along the bluffs of a few streams. These 

 sandstone ledges, however, are of comparatively little economic value, being gener- 

 ally too soft for building purposes. Quarries occur near Nardin, Kingfisher, Hen- 

 nessey, and Luella. In the general absence of building stone, foundations for houses 

 are usually made of brick, and artificial stone may come into use extensively. 



"The rocks of the western area of the Enid consist chiefly of red clay shale, some 

 inconspicuous ledges of soft sandstone, and occasional bands of whitish or greenish 

 shales, which vary from one inch to several feet in thickness. The upper strata are 

 in places highly gypsiferous, and at some localities brine springs issue from them. 

 No attempt is made to separate the eastern and western areas of the Enid formation, 

 except to state that they are sometimes separable locally a few miles east of the 

 base of the Gypsum Hills. 



"The Enid formation is in most places strongly impregnated with mineral salts, 

 particularly common salt and gypsum. In many localities the water from the wells 

 is unfit for drinking, and the people are obliged to use cistern water. 



"In the western area, along the base of the Gypsum Hills, salt measures are 

 prominent. The Little Salt Plain, in northern Woodward County, near the Kansas 

 Line, and Big Salt Plain, in the northeastern part of the same county, are both 

 located in the Cimarron Channel, while the Salt Creek Plain, in north-central 

 Blaine County, is on a tributary of the same river. At the Salt Creek Plain some 

 of the most typical saHne springs in the Territory may be seen. In several canyons 

 at the head of Salt Creek are exposures of a grayish-red, mottled, saliferous sand- 

 stone. This sandstone is often distinctly cross-bedded, and appears to have been 

 tilted; from it issue numerous springs of strong brine. So far as is known, this 

 sandstone is not found elsewhere in the region, and it seems to be a local phase of 

 the clay-shale formation. It is possible, however, that these sandstones are not 

 themselves salt-bearing, but are merely porous strata through which brines from 

 some deep-seated source reach the surface. The water from the springs issuing 

 from the various canyons forms rills, which, in turn, unite to form the headwaters 

 of Salt Creek. 



"Above the level of the Salt Plains, and below the gypsum ledges, there inter- 

 vene 150 or 200 feet of red clay shale, which is interspersed with bands of whitish, 

 greenish, and bluish clay, and local thin ledges of gypsum. 



"The very soft material of which this shale is composed renders it particularly 

 susceptible to the action of the weathering, and the entire thickness is characterized 

 by marked erosion forms. Wherever the cap of gypsum has been removed over any 

 considerable area, or for any great length of time, these shales have been worn 

 away. Perhaps the most common erosion form is that of cones of red clay cut by 

 deep and uneven gullies— regular bad lands structure. Not infrequently rows of 

 these cones are arranged palisade-Hke along the summit of a fast-disappearing ridge, 

 into which gullies are eating their way. In the Glass Mountains, for instance, the 

 slope of the bluffs below the gypsum ledges is much cut by erosion. The action of 

 the water has produced a great variety of unusual forms. Small buttes and but- 



