. Annual report of the United States Geological Survey to the Secretary of the Interior . B. GEOLOGIC MAP OF THE TEXAS REGION. 1, Older granite ; 2, Paleozoic and Mesozoic ; 3, Cambrian-Silurian ; 4, Carboniferous; 5, Permian;6, Jurassic; 7, Lower Cietaceous; 8, Upper Cretaceous; 9, Nonmarine Tertiary ; 10, MarineEocene; 11, Coast Neocene; 12, later igneous. UNIVERSITY ef-JLLIKOIS HILL.] RELATION OF FORMATION TO RELIEF. 31 tion; correspondingly, the minute configuration of the stream valleys,valley plains, escarpments, and man}* of the level prairies borderedor surrounded by scarps also depend
. Annual report of the United States Geological Survey to the Secretary of the Interior . B. GEOLOGIC MAP OF THE TEXAS REGION. 1, Older granite ; 2, Paleozoic and Mesozoic ; 3, Cambrian-Silurian ; 4, Carboniferous; 5, Permian;6, Jurassic; 7, Lower Cietaceous; 8, Upper Cretaceous; 9, Nonmarine Tertiary ; 10, MarineEocene; 11, Coast Neocene; 12, later igneous. UNIVERSITY ef-JLLIKOIS HILL.] RELATION OF FORMATION TO RELIEF. 31 tion; correspondingly, the minute configuration of the stream valleys,valley plains, escarpments, and man}* of the level prairies borderedor surrounded by scarps also depends upon the relative hardness of therocks. The inclination of the rock sheets is an important factor in pro-ducing relief. Where these are horizontal or but gently inclined thetendency is toward plane surfaces with vertical cliffs bordering thedrainage grooves; where steeply inclined, rugged mountainous formsresult. Consolidation, friability, cohesion, solubility, and porosity modifythe relief in various ways. Loose sands are heaped by the wind intolow hills or dunes; unconsolidated cl
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