The natural order of sequence in considering the relations between the Mesozoic floras of North and South America must be the Triassic, the Jurassic, and the Cretaceous.
Rocks of Triassic age are known in many and widely separated parts of the world, and they are of great thickness, which implies a varied and relatively long-continued period of geologic activity. It is also evident from the thick deposits of coal known at several points, and in other ways, that vegetation must have been fairly abundant and considerably varied in character; yet the determinable forms of plant life that have thus far been recovered from the Triassic are surprisingly few in number—in fact, it is doubtful if the known flora far exceeds 300 species. This is, of course, to be largely attributed to the fact that much of the deposits were laid down under marine conditions, where one would hardly . . .