BOOKS AND CURRENT LITERATURE 191 



plainly .to the existence in Alaska during the Ice Age of conditions more 

 favorable for both plant and animal life than are those of the present 

 time, and additional data are given pointing not only to the existence 

 of a geologically recent land bridge between Asia and America by way 

 of Bering Strait but also more definitely assigning its date: "during 

 Pliocene times until the commencement, or perhaps until the end, of 

 the early part of the Pleistocene period." According to the author 

 "there is no indication of any wholesale destruction of the fauna during 

 the Glacial Epoch, followed by a recent introduction from the south." 



In the Rocky Mountain region and in the arid regions of southwestern 

 North America occur, as is well known, various species of plants which 

 are not met with in southern Mexico, Central America and the northern 

 Andes, but which reappear in the extreme south of South America. 

 Moreover, as early as in mid-Cretaceous times 75 per cent of the 

 known plants of Argentina were characteristic types of the Dakota 

 group flora of North America, which must be taken to indicate commu- 

 nity of origin. From these and numerous other data the conclusion is 

 reached that a direct land bridge between western North America and 

 Chile probably existed in Cretaceous and early Tertiary times, and it 

 even seems likely that various species of plants of those remote times 

 have persisted to the present day, with the discontinuous distribution 

 already indicated. 



In like manner the steadily accumulating evidence derived from dis- 

 continuous distribution gives support to the assumption that, far more 

 than leading geologists have admitted, the continents were connected 

 by land bridges by which interchanges of plants and animals were 

 effected as early as Tertiary times and even earlier. Such bridges are 

 believed to have connected Chile and Patagonia with Mexico and Cal- 

 ifornia, the West Indies and areas both to southward and northward 

 with the Mediterranean region, South America with Africa, southwest- 

 ern North America with eastern Asia, and still other connections are 

 traced with varying degrees of probability, approximating to certainty 

 in some«cases, as for instance the early continuity of land between New 

 Zealand, South America and South Africa. 



Without essaying the task of following the author further in his re- 

 markable marshalling and interpretation of facts similar to those already 

 noted, it may be said that his work, however modestly and in parts 

 tentatively offered, is nothing less, as stated in its concluding words, 

 than an attempt "to show how the gradual evolution of our continents 

 and the former changes of land and water can be demonstrated by a 



