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122 SE Faldeo of Pampa Pelada. This section, indicated to us by Pi�tnitzky + visited with him, shows marine trans- gression over the Mammal-bearing tuffs on the NW side of the Rio Chico, where Ameg- hino says it does not occur. A is unquestionably part of the Notostylops- Pyrotherium series, but the few bones found were not identified. B is a tuff similar to those below, but is marine (a fact first established by our visit- P. + Feruglio believed it terrestrial). D is obviously marine. Pi�tnitzky be- Section on lieves (tentatively) slope of that there is an Pampa Pelada unconformity between nr. Rio Chico, B + C, B being on road from Patagonian, C terres- Paso Niemann. trial, + that D is Rionegrense. It is not certain to me from field re- lations only that these are not all part of one trans- gression. (Written Sideways: D Bed full of Ostrea ? d'Orbignyi Yellowish sands C Gray sands, finely stratified horizontally. B Massive gray tuff, with bryozoa, Turitella, and shark teeth. }Mammal Bones, Tuffs indeterminate A No exposures) 390 123 391 392 IN 393 BOOK TWO 394 395 396 397 398