104 ANNAL8 NEW. YORE ACADEMY OF SCIENCES 



ically studied, offer evidence against instead of for a continuous Gond- 

 wana Land. In fact, all of the alleged evidence has been derived from 

 the static viewpoint of plant and animal geography which has led to 

 many erroneous views of correlation and geology of South America. 

 There was not found a single case in the evidence for a continuous Gond- 

 wana of any age or location in which the distributed ancestral form was 

 actually known. 



In view of all this, I have been forced to change my former belief in a 

 connection between South America and the eastern hemisphere, because 

 the geological evidence overwhelms the biological hypotheses. The frag- 

 mentary positive evidence in a few individual cases may not always indi- 

 cate that this view is true, but when both positive and negative evidence 

 derived from botany, zoology, paleontology and geology is carefully 

 weighed and due allowance is made for the imperfection of exploration 

 and the imperfection of the fossil record, the evidence is decidedly against 

 the hypothetical connections. 



I therefore believe that continental forms have originated and dis- 

 persed over three great tongues of land which have always extended south 

 from the northern hemisphere. These three great tongues of land have 

 been connected and disconnected from time to time, and it is possible 

 that they were connected at the south pole at some time previous to the 

 Carboniferous epoch, but so far there is little or no evidence for such a 

 view. 



There have been from time to time possibilities of plants and animals 

 interchanging between these three tongues of land by way of the north- 

 ern hemisphere. 



In a word, we do not accept the theses of hypothetical land-bridges 

 and invasions of the sea; we fail to appreciate the weight of the evidence 

 in favor of these theses, and we look forward with keen interest to the 

 results of coming years in field work and in dynamical studies especially 

 in the regions of zoodistributional transitions, i. e., Central Asia and 

 northern South America. 47 



47 It is in a way extremely unfortunate that so much work is done in regions like Pata- 

 gonia and southwest United States in order to prove a theory which can only be proven 

 by hunting the deposits in northern South America. 



