FONTAINE.] THE OROVILLE FLORA. 865 
Of these 28 different plants—for they are different, whatever may 
be their true place and affinities—14 are new and of no value for fixing 
age by identity. Counting out the undetermined cone, we have only 
12 forms that may be compared with previously known ones. Seven 
of these, viz, Cladophlebis spectabilis, O. argutula, C. whitbiensis 
tenuis var. at, Thyrsopteris Maakiana, Podozamites lanceolatus, Podo- 
zamites lanceolatus latifolius, Pinus Nordenskiildi?, were found by 
Heer in the Jurassic formation, which he regarded as middle Brown 
Jura, which is about the equivalent of the lower Oolite of Scarborough. 
Of these, Cladophlebis spectabilis and Podozamites lanceolatus are espe- 
cially valuable for fixing age by determination of identity. Clado- 
phlebis spectabilis, as stated in the notice of the species, is a type not 
common among ferns, and it has a character that enables its identity 
to be fixed by a small amount of material. The Podozamites also is 
a form readily distinguished, while it is, at Oroville, very abundant 
and well preserved. Three of the plants whose identity with pre- 
viously known ones is more or less fully made out are: Didymosorus? 
bindrabunensis?, Oladophlebis indica?, and Pterophyllum rajmahalense? 
They were all originally made known from the Rajmahal beds of India. 
These Feistmantel regards as of Liassic age. None of the forms from 
Oroville are well enough preserved to enable us to make a very close 
comparison with the India fossils. Although the establishment of 
identity is not certain, yet the existence of a close resemblance in type 
has considerable value in determining age. This fact will be again 
noticed farther on. The Pagiophyllum type of conifer is highly char- 
acteristic of the Jurassic, and it is significant that the Oolitic form P. 
Willéamsonis is the only conifer of importance in the Oroville flora. 
Tt will be noticed that the proportion of conifers in this flora is remark- 
ably small, the ferns and cycads making up most of the plants. This 
isa feature that is more characteristic of the Older Mesozoic than of any 
other flora. The only remaining plant possibly identical with a known 
one is the doubtful Sagenopteris Nilsoniana. This Sagenopteris is 
most characteristic of the Rhetic. The Oroville specimen, standing 
alone and being doubtful, can not have much weight. 
Turning now to the plants which must be regarded as new, we find 
that, although we can not derive any evidence from their identity with 
known forms, they are not without indications that may be taken as 
evidence of age. As was stated before, the prevalence of a particular 
type is of value as indicating age. We find that certain types abound 
in the floras of particular ages, and are absent or rare in others. For 
example, the Alethopteris, Neuropteris, and Pecopteris types of ferns 
are most characteristic of the Carboniferous. The Thyrsopteris and 
Cladophlebis type is conspicuous in the Mesozoic and most character- 
istic of the Jurassic. 
