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by anatomical adaptations to environment. The third chapter gives 

 the leading facts of geological history, and is designed for botanical 

 readers. The next chapter discusses the various methods for the 

 preservation of plants as fossils ; structure unmodified, as in fossil 

 soils and forests ; carbonization ; incrustation, as travertine ; casts ; 

 petrifactions. The relative rarity of plant fossils is due to their soft 

 structure and land habitats. Chapter v is exceedingly interesting 

 and valuable, as it demonstrates the enormous difficulties and sources 

 of error, such as (i) the danger of depending too much on external 

 resemblances, since many forms from algse up to seed plants may look 

 alike even in modern forms, much more in fossils ; (2) fragmental 

 preservation — this is much more common than in animal fossils, and 

 also leads to much more error, since a plant often can be identified 

 only in fruit ; (3) decorticated trunk and pith cylinders ; (4) resem- 

 blance to animals or animal tracks and mineral deposits. 



After a chapter on nomenclature, the author takes up the plants by 

 groups. In this first volume he treats only of the Thallophytes, Bryo- 

 phytes, and some Pteridophytes. Among the algse there is an abun- 

 dance of undoubted fossil blue-green algse, forming deposits of 

 travertine and possibly oolite. Professor Seward thinks that similar 

 forms probably represented the first life of the Algonkian. Because 

 of their siliceous tests there are vast deposits of diatoms, mainly from 

 the Cretaceous on. Of the larger marine algse those forms are 

 especially preserved which are covered during life by calcareous incrus- 

 tations, especially the corallines. Many plants of all kinds and many 

 mineral deposits, rill marks, and animal tracks have been referred to 

 the algse, and especially to the fucoids. Among fungi there are 

 abundant evidences of fossil bacteria, but the higher forms are rare, 

 though found in the Carboniferous and Tertiary. The liverworts and 

 mosses are poorly preserved and difficult to identify. Of the Pterido- 

 phytes, the author considers in this volume only the equisetales and 

 sphenophyllales. Both of these groups are abundantly preserved and 

 well known. At the close of the volume is an excellent bibliography. 



This work of Seward's has at least three features to commend it 

 that are by no means common to all books on paleobotany. It is 

 extremely cautious in its staiements; many forms commonly described 

 are either classified tentatively or omitted altogether. There are not 

 so many startling allusions to high-grade plants in the early ages, but 

 there are more real facts on which to base safe conclusions. Another 



