KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 5l|. N:o 3. 11 
The other species, however, present no difference in regard to the age. The Born- 
holm strata in which D. Johnstrupt occurs are regarded as Liassic, but they contain a 
considerable number of species identical with such from the Middle Jurassic of Eng- 
land and other countries. D. Hawelli is found in the very type-formation of the 
Middle Jurassic — the Lower Oolite of Yorkshire. j 
The Tekenika specimens of Dictyozamites may thus safely be held to indicate 
that the deposit belongs to the Jurassic, most probably perhaps to the Middle Jur- 
assic. The fragment of Sphenopteris [cf. S. (Coniopteris?) hymenophylloides], which 
in itself proves nothing, agrees well with the result thus arrived at. 
The Jurassic deposit of 'Tekenika offers the only clue al present available to 
the age of the south-western zone of the Fuegian cordillera. The great »>slate-forma- 
tion» of Tierra del Fuego and southern Patagonia has been the subject of much dis- 
cussion. MNince STEINMANN (1908, p. 193) has shown that the supposed Jurassic and 
Cambrian fossils collected by the French »Mission scientifique au Cap Horn» have been 
wrongly determined, only Cretaceous faunas are known from this wide-spread forma- 
tion. These faunas have almost all been collected — by DARWIN, STEINMANN, HAU- 
THAL and others — in southern Patagonia. The only information existing on the 
age of the »slate-formation> south of the Straits of Magellan is offered by the few 
fragments collected on Staten Island by the French expedition and identified by 
STEINMANN (I. c.) as belonging to a bivalve, probably of the genus Inoceramus. The 
»slate-formation» assumes a more and more metamorphic character as the crystalline 
zone in south and west is approached, and in Hoste and Navarine Islands it consists 
of phyllites and mica-shists (cf. QUENSEL 1911, p. 16). It is impossible at present 
to state what relation the »slate-formation» has to the fossiliferous deposit of Teke- 
nika. It is possible that the latter beds belong to the same great series; but it is 
more probable that they represent a different and considerably older stratigraphical 
unit. The >»slate-formation» so far has yielded only Cretaceous faunas of which the 
oldest is the one collected by DARWIN at Mount Tarn and regarded since that time 
as Neocomian or Aptian. This fauna must be separated from the Tekenika beds by 
a considerable space of time, since there is no reason to regard the latter as younger 
than Middle Jurassic. At any rate, it is certain that the fossiliferous deposit at Teke- 
nika represents the oldest horizon at present known in the Fuegian cordillera. it 
may be hoped that it will offer a clue to the stratigraphy of the highly disturbed 
sedimentary rocks which border to the western and southern crystalline zone. Bahia 
Tekenika no doubt offers the best starting-point for a study of these rocks; and from 
the observations made during my only too short stay there I think it may yield 
very good results. 
The Jurassic of Bahia Tekenika stands at present rather isolated within the 
Andes of southernmost South America. It is not till we come to the northern border 
of what is usually called Patagonia, in the region of Rio Limay, that deposits of a 
corresponding age are again found to contribute to the structure of the cordillera. 
It is possible that the Mayer River beds (see below), north of Lago San Martin, may 
reach fairly low down into the Jurassic; but this is as yet an open question. 
