PALEOBOTANICAL EVIDEXCE 507 



upper Algonkian time as warm, perhaps subtropical. Coordinative data 

 from the side of animal life consist of about five types of trails or bur- 

 rows and fragments of a supposed crustacean {Beltina). 



Camhriun and Ordovician floras. — Plant life of Cambrian and Ordovl- 

 cian time is practically unknown. Walcott speaks of having seen a 

 number of algal forms in certain Cambrian formations that appear to 

 be at least generically similar to those described by him from the Algon- 

 kian, but they are still undescribed. He adds : "The field of investiga- 

 tion, however, is a large one, and promises most interesting results.'^ 



An appeal to the animal life of the time shows that it was becoming 

 increasingly abundant and diversified, and, so far as I am able to learn, 

 it indicates warm waters, wide — practically world-wide — distribution, 

 and absence of marked climatic differentiation. As an example, men- 

 tion may be made of certain stony corals (Archgeocyathidae) of the Cam- 

 brian that are found in California, Labrador, Xew Liberia (70° X.), 

 Sardinia, Spain, Australia, and Antarctica. 



There is every reason to suppose that plants were equally abundant 

 and equally undergoing diversification; but, as they were still confined 

 to an aqueous habitat, they have left little trace of their existence, unless 

 they had the power of secreting lime. 



Silurian floras. — Our knowledge of the plant life of the Silurian is 

 still extremely limited. It consists in the main of marine algae, and of 

 these some 15 or 20 supposed generic t}'pes are recognized. A few oi 

 the best defined ijl^es are thought to indicate with a reasonable degree 

 of certainty the presence of the modern groups Caulerpaceae, Floridaceae, 

 and Fucacese, but the majority are so poorly defined that it is unwise, 

 if not impossible, to attempt to refer them with certainty to living groups. 



Devonian floras. ^Tlie coming of Devonian time witnessed one of the 

 most important events that has been recorded in the entire history of 

 plant life. It was then for the first time — at least in force — that plants 

 emerged from an aqueous habitat and began their conquest of the land. 

 In early Devonian time the land-masses were in the main low and fiat, 

 with low coasts and deep bays bordered by broad marshes, in which the 

 surface was intermittently covered by brackish or fresh waters that seem 

 likely to have offered a favorable setting for this momentous transforma- 

 tion. White ^ says: 



"It seems permissible to suppose that tlie ancestors of the laud plants were 

 amphibious, perhaps growing where exposed only at the recession of the tide. 

 It is, I believe, probable that these early plants were but sparsely foliate, 



^ David White : Upper Paleozoic floras, their succession and range. Outlines of geo- 

 logic history, 1910, p. 140. 



