KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 51. N:o0 3. 15 
(3) Immediately above the conglomerate lies a fairly hard volcanic tuff. It 
is generally bluish white, but other colours occur too. It contains a great percentage 
of lime, which has given rise on a lower level to considerable deposits of recent 
caleareous tufa close to the estancia of Mr. FRANK. 
(4) On the top of the tuff follows a fairly coarse yellowish white sandstone 
which was exposed only to a thickness of rather less than a hundered meters. Above 
this sandstone there is a gap in the series, owing to covering by waste, but about 
100—150 m. higher up in the slope commences one of the most important divisions 
of the whole meseta series. 
(5) These strata consist of black slates which contain calcareous nodules and, 
in the upper portion, intercalations of rocks like those of the following higher beds. 
This series of slates is very fractured and somewhat disturbed by faults, but has the 
same general dip of 20—30” E. as the next lower and higher members of the series. 
The slates are fossiliferous, but very sparsely: only single specimens were found at 
great distances from each other, so that their position in regard to each other could 
Scale 
NERE a ER RE RESA 
0 200 400 600 800 1000 m 
Fig. 3. Diagrammatical section of the western border of the meseta east of Bahia de la 
Lancha, Lago San Martin. For explanation see the text. 
not be ascertained owing to the disturbed state of the strata and the gaps caused by 
waste-covering. The upper limit of the slates was not exposed, but it is evident 
that the series has a thickness of more than 500 m. Most of the fossils were found 
in the upper part, in which already occur intercalations of arenaceous sediments 
resembling those of the next higher strata. This division and the following one are 
undoubtedly very closely connected. 
(6) The highest division of the series is composed of thick beds of rather coarse 
yellowish sandstones. The rock, though it always has a yellowish colour, appears 
somewhat variegated because the different shades vary from yellowish white to a 
rusty tint. It appears to contain volcanic material in varying quantity, having often 
a rather tuffoid aspect. Fossils are very rare in this rock and consist mostly of 
rather badly preserved bivalves. The thickness of the series cannot be determined, 
because the uppermost beds disappear, with an easterly dip, underneath the basalt, 
but the exposed portion measures probably about 500 m. at least. 
(7) The whole sedimentary series is capped by the basalt which forms the sur- 
face of the meseta. It has a very varying thickness and rests unconformably on 
the denuded surface of the sedimentary series. The strata of the latter have, on 
