10 
INTERPRETATION OF FOSSIL PLANTS 
or fresh-water origin of the containing sediments, are, exclusive 
of calcareous forms, so rare or so poorly preserved, or so poorly 
understood, as to be practically valueless. The calcareous forms, 
such as the oogonia or other traces of fresh-water forms, or the 
lithothamnias and coralline algae of marine waters are better 
understood and furnish more definite objects for study, but when 
present in a formation furnish needless corroborative evidence of 
the origin of the containing sediments, since the associated animal 
organisms usually offer conclusive evidence as to the nature of 
the deposit. Coralline algae and their allies are, like bryozoa and 
corals, indicative of clear water and the absence of any consid¬ 
erable amount of turbidity, which means generally, slight or slow 
run-off from the land, and the absence of salt-carrying rivers 
debouching in the basins of sedimentation. Slow run-off from a 
land of mature topographic form is not to be distinguished from 
slight run-off due to actual deficiency in rainfall, therefore noth¬ 
ing can be said as to actual precipitation in this connection. 
Bacterial action, such as the influence and effects of nitrifying, 
denitrifying, iron or sulphur bacteria, will not be discussed, since 
it constitutes a separate field, which at the present time, belongs 
more properly to sedimentology rather than to paleontology. Nor 
will more than incidental reference be made here to the lower 
orders of plants, the present note being consequently restricted 
for the most part, to the more common and better understood 
vascular plants, the vast majority of which are terrestrial in their 
habitats. 
In considering the latter it may be noted that the interpretation 
of fossil plants in terms of their environment becomes indefinite 
or definite according as one is dealing with the more ancient types, 
for example those of Devonic times which botanically have no 
closely related existing forms; or with fossil plants, like those of 
the Tertiaries whose near of kin are still living. Hence it is 
possible to use the prevailingly angiospermous floras of the Ceno- 
zoic Period with much greater precision than can be obtained with 
Paleozoic or Mesozoic floras. 
With respect to fossil flowering plants, genera which still exist 
in great specific variety tend to occupy a variety of habitats and 
live under varying conditions of rainfall and temperature, and are 
hence inconclusive in attempts at the precise evaluation of the 
