RECURRENT TETRAHEDRAL DEFORMATIONS AND 

 INTERCONTINENTAL TORSIONS. 



By B. K. EMERSON. 



(Received May 5, 1917-) 



Starting a long time ago to write a review of a very interesting 

 and remarkable book I have woven so much of my own musings with 

 the text that I may not well put upon the author the responsibility 

 therefor. 



The book in question is " Die Entwickelung der Kontinente und 

 Ihere Lebewelt. Ein Beitrag zur Vergleichenden Erdgeschichte ; 

 von Dr. Theodor Arldt, Oberlehrer an der Realschule in Radeberg, 

 mit 17 Figuren und 23 Karten." Leipzig. Wilhelm Engelmann. 

 1907. 729 pp., large 8°. It is a ponderous volume comparable to 

 Walther's " Einleitung " or Suess' "Antlitz der Erde," but more 

 systematized, and condensed to the limit ; so that an exceedingly 

 great amount of painstaking and acute research, covering many 

 diverse fields, is brought into remarkably small compass. 



Just two thirds of the book is devoted to a biogeography of the 

 past and the present. After chapters on method comes a general 

 survey of the distribution of plants and animals in the present and 

 Cenozoic, in the Mesozoic and in the Paleozoic, with discussions of 

 their evolution and many " Stammbaume " to summarize this evo- 

 lution. 



The principal purpose of the study is to get all the light which 

 the distribution and probable migrations of the different classes of 

 animals and plants can throw upon the evolution of the continents. 

 A first chapter takes a position adverse to the so-called " permanence 

 of the continents." Only certain large portions of the great ocean 

 seem to have been permanent. 



This section is illustrated by a full and clear chart of the bio- 

 logical provinces and regions and five charts which show the migra- 

 tions of the families of the vertebrates, and ends with two valuable 



445 



