14 T. G. HALLE, MESOZOIC DEPOSITS AND FLORAS OF PATAGONIA AND TIERRA DEL FUEGO. 
the section is of importance because of the marine fossils, and the information which 
it affords in regard to the probable position of the plant-bearing beds in the series. 
The different strata in this section will here be described in ascending order (text-fig. 3). 
(1) On the shore of the lake, the surface of which according to the map of 
the Argentine Boundary Commission, lies 200 m. above sea-level, the basement of 
the sedimentary series of the meseta crops out. It consists of a very ancient-looking 
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a DELDEPOSITO 
VAN 
Fig. 2. Sketch-map of the region north-east of Lago San Martin. After the Argentine 
Boundary Commission. Scale 1:400000. Heights in metres. 
formation of highly inclined, hard and metamorphosed rocks, quartzitic sandstones 
and dark phyllitic slates. 
(2) Unconformably upon the denuded surface of this formation rest the basal 
layers of the meseta series, a hard consolidated conglomerate which contains pebbles 
of the underlying rocks. This conglomerate, which reaches a thickness of about 15 m., 
dips only 20—30” E., and is conformably overlaid by the following beds of the meseta 
series, from which, however, it differs markedly through its greater hardness. 
