3i6 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 niudcracks — 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 ostracodenns, 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 forenmners of 

 ferns and their allies, and the lower fern-like gymnosperms with 

 an undergrowth of soft thallose fornis, 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 



