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156 sands. 4. Pale clays, massive, grey, pinkish, greenish, and fine to coarse x-bedded sands, usually white or grey, but often greenish or pink to red. Although physically similar and not separable at present, these include two parts probably quite distinct in age: a. An upper series in which the pillar bed and mammal sand- stone are intercalated. b. A lower series including true Banco negro. In (2), probably in its lower part only, are also seen two very special types: thin widespead white beds supposed in the field to be diatomaceous earth (profiles CA, CF), and finely laminated shales with local plants and fish (CF, also occurs although less prominently + without fossils in CA). We have identifiable mammals from 1,2, + 4a which should help to clear up the sequence. This sequence is not certain in field observation, but appears to be in the order of the above list, top to bottom. 157 1 clearly forms the top of the series, being the only type found near or at the contact with the Patagoniano and in general not occurring elsewhere. 4 similarly clearly forms the base. The presence of a much disturbed block of this type of sediment among the tuffs of type 1 (Profile CE) can only be due to faulting. The relations of types 2 + 3 to each other + to 1 + 4 constitute the major problem. Type 2 has a thickness of not less than 200' in profile CF, Type 3 not less than 125' in profile CD. The transition from 2 to 3 was nowhere clearly observed, being either obscure or along a clear or probable fault. They often occur laterally at the same level, as in profile CA, but with such sudden change that they can hardly grade into one another directly in these cases, although they may do so to some extent in the series as a whole. It seems highly probable, not proven, that they intergrade somewhat