[PENHALLOW] A REPORT ON FOSSIL PLANTS 313 
ton (38: p. 240) and now universally admitted, it now becomes possible 
to recognize the fact that the numerous instances of the occurrence of 
this tree in Spitzbergen (22: p. 57), Grinnell Land (24: p. 23), 
Siberia (25: p. 33), Saghalien (13: p. 22), Alaska (39: p. 878 and 51; 
p. 214), as well as in Greenland itself (23: p. 60; 26: p. 9; 28: p. 
463, and 29: p. 89) give unquestionable proof of its wide spread and 
abundant occurrence throughout the Eocene of America as well as of 
Europe. While, therefore, it is a form essentially typical of both the 
Eocene and Miocene, its greater abundance in the former implies a 
vigor of development which it appears to have lost in more recent 
times, although this does not of necessity permit us to conclude that 
its presence in a given horizon is more indicative of the one age than 
the other, a relation which must be finally established by collateral 
evidence. 
Pinus columbiana does not, in itself, afford decisive evidence as 
to the nature of the horizon from which it comes, but a review of the 
distribution of the genus Pinus as now known may serve to suggest a 
reasonable conclusion. 
The genus Pinus, as given by Knowlton (37), embraces nineteen 
species, most of which are defined specifically, ranging from the Dakota 
Group through the Cretaceous and Tertiary to the Pleistocene, where 
they become identified with existing species. But to these we may 
add six species of Pityoxylon, some of which are of Upper Cretaceous 
age, but most of which are Tertiary forms most largely represented in 
the Eocene. More recently, Knowlton (35) has also recognized the 
occurrence of the wood of Pityoxylon aldersoni and P. amethystinum 
in the Upper Miocene of the Yellowstone National Park, while on the 
other hand a recent publication by Ward has brought to light Pinus 
leei, Fort. (57: p. 570), from the Older Potomac Formation of Vir- 
ginia, a case which parallels that recorded by Heer of P. crameri, Heer, 
from the Kome beds of Greenland. While some of the species of 
Pinus thus referred to are recognizable through their wood structure, 
many others are known only through their foliage, and, although these 
latter are designated by distinctive names, it is not altogether certain 
that they are specifically distinct or that they are different from species 
represented by other remains with which it is at present impossible to 
identify them. A very large number of known species are represented 
wholly by seeds, and this is particularly true of the numerous species 
which Heer describes from the Eocene of Greenland and other Polar 
regions (22:* Vols. I-VII). Inasmuch as such seeds are representative 
of the fruit, they may be directly connected with the cones, which are 
