; 
Dr. J, 8. Newberry on Ancient Vegetation of N. America. 215 
having been common to the two sidesof the Atlantic. The rela- 
tive number of identical species has, however, it seems to me, 
Tecent plants and recent or fossil animals. I have a conviction 
that the progress of science will considerably diminish the pro- 
portion of identical species ; a closer scrutiny and more extensive 
comparison of specimens resulting in the discovery of constant, 
nrg inconspicuous characters which shall be ultimately con- 
ceded to be specific. 
It is true aa that in molluscous paleontology, recent geology 
and botany, the number of species common to the two continents 
has been considerably reduced of late years; a large number of 
on closer 
differences, 
2d. The Permian, Triassie and Jurassic rocks have hitherto 
furnished us but few species for comparison, but the material is 
This statement will ise man : for the flora generally as- 
ctibed to the Chalk pee: 5 ea different from that of the 
