3 l6 
The Ohio Naturalist. 
[Vol. XI, No. 6, 
growth. This relative absence of fossils, together with the char- 
acter of the sediments, the frequent aeolian crossbedding and 
frequent mudcracks— are the mark of periods of exposure; they 
point to near-shore deposits if not to land origin, and to conditions 
of aridity with tropical climate. This does not mean, however, 
that a prolific vegetation and perhaps of an advanced order did 
not exist. Though nothing that can be called a land flora existed, 
or at least is yet known, the plants of the following period show 
such marked differentiation and the ancestral relations are so 
uncertain, that a long previous history, or else a rapid evolution 
and extinction of intermediate forms would be the only alterna- 
tives on which to base an interpretation. A number of species 
common to Kentucky, Michigan and some parts of Europe have 
been described; among them are Buthrotrephis ramulosa (16), 
which bears a close resemblance to Galium (Bedstraw), and 
Trichophycus venosus, regarded as a plant from the Eden and 
Lorraine formations. The animal fossils have many character- 
istics in common with the European Siluric. 
The sea again invaded the land and submerged it wholly. A 
general period of quiet prevailed during the larger part of the 
following, the Devonian Age. Toward the close of the Mid- 
Devonic renewed emergence was accompanied by erosion. The 
era includes the Columbus and Delaware limestones, and the 
Olentangy and Ohio shales. Where the changes in the relations 
of land and water were favorable, a rapid intercontinental migra- 
tion and expansion of life followed, checked only by barriers and 
by occasional submergence. The record of plants (18) is too 
imperfect in Ohio for definite discussion, but fossil evidences show 
that gigantic marine algae were abundant in the seas together 
with fish and ostracoderms, while on the land-islands then exposed, 
there were insects, and mollusks, and in the flat lowland surfaces 
were broad marshes covered with plants, the larger number of 
which were herbaceous and highly differentiated. The Devonian 
plants of contiguous areas show no annual rings to bear evidence 
of seasonal changes in temperature or intervals of prolonged 
drought (25). The flora is far richer than that of the Silurian, 
and of great botanical interest, since in this period occurred great 
migrations of plants from the Arctic regions, and the development 
if not the actual beginning of land plants. These facts suggest 
distinct edaphic as well as other environmental changes. The 
great inland basins contained a vegetation archaic in many 
features yet not unlike that now living in swamps and in the 
tropics. The plants were largely the primitive forerunners of 
ferns and their allies, and the lower fern-like gymnosperms with 
an undergrowth of soft thallose forms, very much like the liver- 
worts of today; their decay was accelerated by bacterial action 
(22). The Devonian types were in many respects similar to those 
