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P. 216 From p. 214 Is ca. 105' above the arg. fis. But below it are two or more thinner beds of similar character, one near the level of that on the other side of the Canadon. It seems to me impossible to assume (as Feruglio) that a single "tosquilla" bank can be distinguished & to infer an unconformity from its variation in level. Mammals, although so few in number, may be found either above or below the main tosquilla. At the place where HB was taken the Patagoniano was completely eroded away in the Pleistocene, although it occurs nearby. The Pleistocene deposit, Tehuelche, consists chiefly pf typical rodados in a sandy matrix, cemented very hard and looking very like artificial concrete, also grey sand, some cemented and some soft. These rocks contain broken pieces of Ostrea hatchem, but no original marine fossils so far as observed. They are approximately 300' above sea level. P. 217 PUNTA NAVA Here on the SE side of the Mazaredo uplift a section similar to that on the NW side reappears (profile TA). At the base are silicified tuffs identical in appearance with the argile fissilaires of Canadon Lobo. Above are tuffs and tuffaceous clays, also of the same character as those at the l;atter locality, & then the Patagoniano. One the NW sideour work & all previous publication agrees that only Notostylopense fossils are found. Similarly on the SE only Pyrotheriano. Three interpretations are possible: 1. The Pyrotheriano has been removed on the NW by pre-Patagonianoerosion. The silicifies tuffs of the SE are bot true argiles fissilaires, but a facies between the fossiliferous Notosti & Pyroth. This apparentely was Ameghinos view. It is unlikelybecause of the identity in character of the arg,fis. & the SE silicified tuff & the slmost continuous interveining exposures. (see) p. 220