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IOWA ACADEMY OF SCIENCE 
The title was first applied by Hill* to the Tertiary deposits which 
veneer the even, seaward sloping plain of western Texas and 
eastern New Mexico. The thickness of the formation is about 200 
feet. All of the beds are to be regarded as of fluviatile origin. 
*Bull. Geol. Soc. America, Vol. Ill, p. 87, 1892. 
