[MATTHEW ] A BACKWARD STEP IN PALÆOBOTANY 121 
tered in the successive epochs of geological time in the same region. The 
reappearance of the Little River flora in the Riversdale terrane in Nova 
Scotia, at a later period in the Maunch Chunk group in Ohio, Arkansas 
and the South Atlantic States, and still later in the Pottsville of Penn- 
sylvania, would tell us not necessarily of cotemporaneous deposits, but 
of corresponding conditions of temperature or habitat or of both, which 
enabled these types to survive to a much later time than had been sus- 
pected. The persistence of the Filicoid types is not surprising, seeing 
that their minute spores gave them the facility for spreading rapidiy 
over wide areas of the earth’s surface where soil and climate were con- 
genial. Some of the modern ferns are almost world wide in their dis- 
tribution. <A species that is widely distributed geographically will stand 
a better chance of persistance in time. And ferns which appeared in 
early Paleozoic times, have left descendents even in the Coal Measures. 
We note, however, that some types which may therefore be reckoned 
archaic are dropped by the way. Pstlophyton does not flourish later 
than the Devonian. Megalopteris, a striking type of fern of generous 
growth, was at first known only in the Little River beds, next it was 
found by Prof. Andrews in the Lower Carboniferous of Ohio, in a 
number of species, and Mr. D. White has lately found it sparingly in 
the Pottsville Group (Millstone Grit). It is known nowhere at a higher 
horizon. Archæopteris, though more widely diffused, and of more fre- 
quent occurrence than the preceding genus, has much the same range, 
except that it is of more frequent occurrence in the Lower Carbonifer- 
ous; this however may be due to the prevalance in this group of soils 
and exposure more congenial to it than the other—at least in the north- 
ern regions where most of the species have been found. Species referred 
to Lepidodendron in the Little River Group are small and the trunk 
scars obscure, in fact they are doubtfully of this genus on account of 
the indefiniteness of the stem features. But in the Lower Carbonifer- 
ous a species appears with small though quite distinct scales; this is var. 
elegans of L. corrugatum, considered by some writers as the same with 
L. velthemianum, an Upper Devonian species. But the species of this 
genus with large leaf scars found in the Coal Measures are absent from 
all the lower terranes. Finally, one might refer to that ancient group 
in the Calamaria which includes Bornia or Archæocalamites. This is 
abundant in the Little River terrane, and not uncommon throughout 
the Lower Carboniferous, but quickly falls out of sight above this 
horizon. 
A number of these forms enter the Pottsville conglomerate measures, 
as announced by Mr. D. White, and it is interesting to note that this 
flora shows a much closer connection with that of the Little R. Group 
than do either the earlier or later floras of Pennsylvania. To Mr. White 
