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108 Ca�adon Vaca The ca�adon runs roughly ESE-WNW, entering the valley of the R�o Chico near Paso Niemann. The south side appears to be wholly composed of sandstone + clay of Pehuenche or Chubutiano type and was not investigated in detail. On the slope of Cerro Salpu, above the general level of the south rim, is a small area of gray clay and white to red sandstone overlying varicolored clays and coarse green sandstone. Near the top of this exposure a few fossil bone fragments were found, but they are unidentifiable, and were on the surface. The Tertiary beds with fossils are exposed along the north rim, chiefly from one to six km., more or less, below the Van Wyk house. The nearest extensive exposures (following this rim ESE' from Van Wyk's), profile BA, furnished very numerous isolated teeth and jaws, mostly residual, + a few skulls, etc. in place. The farthest of the more or less continuous exposures, at a place sometimes called locally the Oficina del Diablo (profiles BB, BC) has little residual material but three beds near the base of the tuff are extraordinarily rich in material in place, including a higher percentage 327 109 328 329 IN 330 BOOK 331 TWO 332 333 334 335