KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 5l|. N:O 3. i” 
sketch-map, text-fig. 2). Here the sandstones of division 6 come down to the level 
of the plain south of the meseta, that is, to a level only a little higher than that 
of the lake. The dip of the strata is here towards the south-east and is greater 
than the inclination of the bottom of the gorge, so that, in advancing upwards, the 
next lower division, that of the black slates (5), is encountered. In loose boulders 
of a hard siliceous slate, which have probably come from the lowermost part of 
division 6, a few plant-remains were found. They consist of pinnae of a fern, Glei- 
chenites San-Martini, and probably fragments of a Podozamites. These few fragments 
are of importance only because they occur in a rock similar to the plant-bearing 
slate in the chief locality, c, at Rio Fösiles, and were found in such a manner as to 
suggest that they are derived from the lowermost portion of division 6. At any rate 
they must come from a horizon at no great vertical distance from the boundary 
between 35 and 6. 
A short distance further south-east, at Arroyo Calafate, the sandstones (6) are 
the lowermost portion exposed. In this place there was found in the lower portion 
of the sandstone a fragment of an ammonite which has been described by Prof. 
STOLLEY (1. c., p. 11) as ÄAncyloceras patagonicum n. sp. and considered to indicate 
an Aptian age. Another fragment in the same piece of rock is described by Prof. 
STOLLEY as ?Oppelia (Adolphia) sp. 
In the bluffs forming the western border of the meseta, along the valleys of 
the rivers Fösiles and Carbon, the continuation of the upper divisions shown in the 
section at Bahia de la Lancha can be traced northwards. Advancing in a northerly 
direction from the lake, the lower divisions of the series are found to be covered 
by young deposits, and in the upper part of the Rio Fösiles valley, the sand- 
stones of division 6 form the lowest portion of the series exposed. The sandstones 
appear to have a still greater thickness than at Bahia de la Lancha. 
The best exposure of the sandstones in the Rio Fösiles valley is along the 
upper part of a small tributary to the river, the last but one on the left-hand side 
on the Argentine map (at c on the sketch-map, text-fig. 2). The base of the sec- 
tion exposed lies about 900 m. above the sea. It is possible that lower parts of the 
series are exposed in the bottom of the main valley, but otherwise the lower slopes 
are here covered by loose deposits. In the exposed section, from 900 m. upwards, 
there is no trace of the black slates of division 5, but it is probable that the lower- 
most strata displayed represent the very base of division 6. This may be assumed 
not only because of the great thickness of the sandstone beds exposed but also 
because, in the lowermost part of the section, slates of varying lithological character 
occur as intercalations and even dominate at the very base. These slates, though 
they have a rather varying aspect, are different from the black and very fractured 
rock which forms the bulk of division 5, being harder and siliceous, with a lighter 
bluish grey colour. These slates at the base of the section at c, are referred to divi- 
sion 6, because they are closely connected with and pass over into the overlying 
sandstones of that division, whereas the typical black slates of division 5 are not 
present here. I have no doubt, however, in regarding the lowermost beds of this 
E. Sv. Vet, Akad. Handl. Band 51. N:o 3. 3 
