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56 direction this may be. 4. In a really continuous section, the supposed plane of erosion covered by Notostylopense is never seen. On the contrary, the beds which actually lie in the main barrancas at the top of the a.f. are invariably parallel to those above. In the rarer cases where lower Notostylopense is preserved in the tilted blocks, it is also tilted + still parallel to the a.f. The 4th fact seems to remove all evidence for the supposed post-a.f. + pre-notost. folding[explanation A] proposed by Keidel, Windhausen. The claimed angular unconformity is here a mere illusion, vanishing when the Beds are more closely studied. The other observed facts, while not absolutely conclusive, involve so many coincidences that the very strongly point to C as the true hypothesis: that this steep folding + faulting is not an ancient + tectonic feature extending to the subsurface but is directly related to the present topography + purely superficial: that the wet plastic clays of the Upper Pehuenche have been incompetent to support the blocks of (originally) nearly horizontal arg. fis. outstanding from the bases of these barrancas and that large sections of the arg. fis. have thus moved by gravity slumping on this plastic base, their lower parts generally moving down the slope away from the barrancas, tilting the blocks more or less sharply and breaking them. [Cont. on p. 60] COLI-HUAPI 57 219. Two bad astrapothere teeth on upper channel of prof. A. G.G.S. 1 pack. 220. Frag. skull, with brain cast and some skeletal frags. Middle part of cliff, between profiles J + K, in upper part of tuff Y. G.G.S. 11/11/30. 5 packages. 28780 221. Various isol. teeth and assoc. small lots. As #220. G.G.S. 11/11/30. 1 package. 28846-8 222. Various frags. + 1 fair notostylopid jaw. As #220. J.H. 11/11/30. 1 package. 28881. 223. Very frag. skull in poor condition. As #220. J.H. 11/11/30. 1 package. 28596 224. Good lower jaw, small ungulate. As #210. J.H. 11/9/30. 1 package. 28669 225. Much broken skull. As #220. G.G.S. 11/12/30. 1 package. 28691 226. Small jaw, both sides, somewhat broken, plus frags. from same spot. As #220. G.G.S. 11/12/30. 1 pack. 28687-8 227. 2 frag. jaws and 1 assoc. lots As #220. G.G.S. 11/12/30. 1 pack. 28849-50