'; ?>
click to enlarge
90 the arg. fis. are well exposed. The bedding is parallel to that of the Pehuenche. The basal beds are imper- fectly or patchily silicified. Their contact against the Pehuenche is sharp but not evidently discordant. The thickness, although not exactly measured (needs instrumental survey) is about half that of the beds of similar character at the south of Coli-Huapi. No fossils of any sort. The upper contact is equally sharp, equally concordant. This series forms a thin but sharply defined entity. "NOTOSTYLOPENSE" ? Between the positively identified Pyrotherium beds and the arg. fis. is a series of pale tuffs with a maximum observed thickness of about 100' ? considerably less than S. of Coli- Huapi evidently conformable, with no conglomerates or other indications of even local unconformity. Its contact with the arg. fis. is seen only in profile AB, where it is sharp but parallel. Neither in this profile nor in AA were any fossils found in this bed. In the main barranca this horizon is not exposed, at least in the better exposures on the north side, but occurs in more or less isolated exposures among the mesetitas and zanjones within the embayment. Here it contains usually its lowest exposed 91 member a massive white tuff with some manganese concretions, which has sparse bone fragments. Of the few specimens of value found, all appear in the field to be of Notostylops age. PYROTHERIENSE: In the embayment and along the foot of the barranca at its north side (Profile AC) the base of the Pyrotherium beds is a fairly readily recognizable and constant horizon, varying in color and hardness but generally with a heavy conglomerate of tuff pebbles and with numerous bones. In some places this bed is obviously unconformable on the lower tuffs, at least locally, in others there is no sharp line although the presence of the same bone layer with pebbles and with rolled bone fragments suggests that the unconformity is general in this dis- trict. Following the bed as far as possible, it seems probable that it does not every where lie on the same horizon of the tuffs below, i.e. that the two are only approximately parallel. The observation is not certain, due to the confusing nature of the exposures.