topteris has been found at several localities without Cal- 
lipteris. For example, at Fulda, Texas there occurs a 
florule with Gigantopteris but without Callipteris, which 
I have previously called ‘‘a Callipteris flora without Cal- 
lipteris’’’’. The Fulda florule is certainly Permian. 
Recently Jongmans and Gothan™ have described a 
very similar Gigantopteris flora from Sumatra. T’ngia 
and Callipteris are absent, and the flora is considered to 
be pre-Permian, that is Stephanian, and closely related 
to the oldest Shansi beds (Yemenkou Series). 
The floras of eastern Asia and northwestern North 
America” have a considerable number of plants in com- 
mon. The two land masses lie in proximity, and inter- 
change of forms is inevitable, the rate of interchange 
being determined by climatic factors. In keeping with 
this logical approach to the problem of the distribution 
of Gigantopteris and Tingia, the only former route of 
interchange or migration was by way of Alaska,the Aleu- 
eutian Islands, and Kamchatka. However, according to 
the Wegener Hypothesis of continental drift, which is 
one of the widely held concepts in geology, the problem 
is not so simple. It must be noted that few American 
geologists admit the hypothesis of continental drift, al- 
though the concept is almost universally accepted among 
European and southern hemisphere geologists. The the- 
sis, stated in its simplest terms, involves the splitting 
apart of a single great continental mass into several parts 
—the existing continents—which gradually drifted to 
their present positions. ‘The North American continent 
is assumed to have split off from Europe and is now more 
remote from its former points of contact than ever before. 
As the counterpart of this idea, the distance between Asia 
and western America has been decreasing, so that it is 
now less than ever before.” 
The Belle Plains formation, in which T?ngia oecurs 
[ 186 ] 
