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52 may occur above the continuous arg. fis. type of sediment, intercalated with typical Tertiary-type. Indeed silicified tuffs with nodular concretions, identical in character with the arg. fis., may occur even in the upper part of the Tertiary series. At other times tuffaceous clays similar in coloring to typical arg. fis. but not silicified may be intercalated between the two. These facts and some irregular variation in the apparent thickness of the Notostylopense below an identified guide horizon ("Y") leads not to the conclusion that they are unconformable, but on the contrary that they intergrade so perfectly that the top of the arg. fis. cannot be identified at the same level everywhere. In fact it seems quite possible that the sharp distinction between typical (or rather extreme) arg. fis. + typical Tertiary is due less to original differences than to subsequent probably hydrothermal alteration of the arg. fis. If this be true, the latter is merely a varying of the lower part of the post-Pehuenche sediments which have suffered alteration. The stratigraphy and paleontology of a locality where arg. fis. do not occur will help check on this. The supposed post-Arg. fis, pre-Notostylopian folding is based on supposed angular unconformity between the two. The actual field conditions as observed SSE of Valle Hermoso station, (nr. Ca�adon Pedro), at several points s. of Coli-Huapi + elsewhere on the north rim of the Valle Hermoso, + at the NE end of Pampa Mar�a Sanhima, are as shown below (p. 54): COLI-HUAPI 53 201-300. G.G.S. FIELD BOOK 201. 28882. Assoc. up. + l. jaw frags. small ungulate. Hor. of #77, profile p.32. J.H. 11/6/30. 1 small block, 1 pack. 28701 28889 202. Assoc. up. + l. jaw frags. small ungulate, + another tooth etc. same place, prob. not assoc. Hor. of #78, profile p. 32 J.H. 11/6/30. 1 small block, 1 pack. 203. About 35 isol. teeth + some other frag's. Surface, lower tuff "Y" profile p. 32. G.G.S. 11/7/30. 1 package. 28404 28461 28476 28483 204. Seven partial jaws + assoc. lots. Tuff Y, p. 32. G.G.S. 11/7/30. 1 pack. 28809-15 205. 5 isol. teeth + 2 very frag. jaws. As #204 J.H. 11/7/30. 1 pack. 28816 206. 3 assoc. lots + 3 isol. teeth. As #204. J.H. 11/7/30. 1 pack. 28477 28817 207. Notopithecus jaw. As #78. J.H. 11/7/30. 1 pack. 28718 208. Isolated teeth. Surface as #203. G.G.S. 11/8/30. 1 pack. 28485