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112 fissilaires" as typically developed. The contact with the tuff is sharp and plane as observed in limited exposures. The lowest tuff is also concretionary, nearly two meters in thickness. Above it comes about 4'-5' of thin bedded tuff and sand. The beds are very broadly lenticular, but not cross-bedded so far as observable. With one exception + possibly another, No fossils were found in these two lower beds of the tuff series, but good specimens of the Notosylops fauna occur immediately above the sands. From this point up to the rodados at the top of the pampa the section consists of tuffs and clays of the usual type, with no coarse material or lava. The Notostylopense is very thick here. From fossils identified in the field it can hardly be less than 200', + if, as seems likely, the lot under #403 is also Notostylopense it is over 275', possibly considerably more This area contains a topographic peculiarity in the form of a bench nearly continuous for several kilometers, bounded on one side by the rising slope of the Pampa, on the other generally by a low ridge and then a dissected slope down to the grey clays. See profile on p. 104. It is clearly impossible that this is due to erosion and it can only be explained by 345 113 346 347 IN BOOK 348 TWO 349 350 351 352 353