46 T. G. HALLE, MESOZOIC DEPOSITS AND FLORAS OF PATAGONIA AND TIERRA DEL FUEGO. 
Sphenopteris (Ruffordia?) Goepperti DUNE. 
» patagonica n. sp. 
» (Onychiopsis?) psilotoides (STOKES & WEBB) WARD? 
Asplenites lanceolatus n. sp. 
Ptilophyllum acutifolium MORR. 
Baera cf. australis M”CoY. 
Arthrotaxites Ungeri n. sp. 
Elatocladus sp. 
The most conspicuous feature of this flora is the total absence of dicotyledons, 
which at once indicates that the flora is older than Middle Cretaceous. It is equally 
evident that it is not older than Middle Jurassic; but an attempt to settle exactly 
its age by means of a comparison with other floras gives rather conflicting results, 
notwithstanding the fact that it is derived from one horizon. Those of the species 
which are of the greatest value in this respect appear to indicate prevailing Wealden 
and Lower Cretaceous affinities. It must be stated at once that it is not possible, 
with the present state of the knowledge of fossil floras, to establish any accurate 
subdivision, on a palaeobotanical basis, of the time from the close of the Jurassic to 
the lower Albian. The Wealden flora, as understood by palaeobotanists, embraces 
more or less the whole of this time, several of the characteristic Wealden species 
being found as high as in the Albian of Portugal (SAPoORTA 1894). It is further well 
known that there is a certain disagreement between the palaeobotanical records and 
the usual stratigraphical classification founded on the evidence of the marine faunas. 
The palaeobotanists often advocate an older age of the strata in question than is 
compatible with the marine fossils. This is so also in regard to the Wealden flora 
proper, of which the marked Jurassic affinities are emphasized by most palaeo- 
botanists. Under such circumstances the conflicting evidence regarding the age of 
the flora is not an isolated abnormity; yet it illustrates in a striking manner the 
difficulties attending an exact determination of the stratigraphical relations of the 
floras of this period. 
Of forms determinable with some certainty the following indicate a Lower 
Cretaceous age, viz.: Nathorstia alata, Gleichenites cf. micromerus, Cladophlebis cf. Brow- 
mana, Sphenopteris Goepperti. One of the most important of these plants is Nathorstia 
alata. The species is well distinguished from all others hitherto known, but the genus 
itself affords a valuable clue. Nathorstia is an unusually natural genus, representing 
a very characteristic type quite unique among Mesozoic ferns. It would appear as 
if representatives of such a characteristic natural type, though different in species, 
would be of greater value for comparison than many identical form-species of an 
artificial genus. N. latifolia, which has been examined in detail by NATHORST, is 
from the Cenomanian of Greenland, the species previously described by HEER are 
from a lower horizon, or the Kome beds, considered to be of Urgonian age. The 
Bohemian fern, Drynaria fascia BAYER (1900), which is compared by NATHORST with 
Nathorstia latifolia, is of Cenomanian agé. The Nathorstia-type, as known at present, 
