450 EMERSON— RECURRENT TETRAHEDRAL DEFORMATIONS. 



tinents, and makes it the basis of his classification of mountains and 

 of his explanation of the chains around the Pacific. 



He follows Reyer and Suess in explaining the chains of southern 

 Asia as " Abflussbogen," outflow chains due to flowage down a 

 slope from the elevated coign or shield of " Angara land " or Man- 

 churia. The festoon chains along the east of Asia are " Zerrungs- 

 bogen," dragged chains due to the separation of ocean bottom and 

 land because of the eastward drag caused by the depression of the 

 ocean bottom and its differential eastward motion. These terms are 

 discussed later in this paper. 



Andes and Cordillera are " Stauungsbogen," heaped up chains " 

 caused by eastward pressure of the sunken Pacific ocean bottom and 

 this pressure is transferred eastward to cause the eastward curving 

 Antilles and the submerged South Georgean eastward curve south 

 of South America. 



The sinking of the Caribbean is an accessory cause of the An- 

 tilles and the sinking of the Mediterranean the sole cause of the 

 chains from Alps to Caucasus. 



It is very interesting that the hypothesis of a tetrahedral earth 

 can be thus utilized in the fundamental explanations of the past 

 conditions of the earth and this may be said to add to the arguments 

 in favor of the hypothesis. 



Wholly novel is the suggestion that tetrahedroid may have alter- 

 nated repeatedly with the spheroid. The earth is thus a composite 

 photograph of several tetrahedra, as indicated in the title of this 

 paper. 



In the following the reviewer presents (i) a different explana- 

 tion of the chains in the Mediterranean zone as due to northward 

 flow (rather than to thrust from the sinking of the Mediterranean), 

 an explanation which was advanced in his presidential address, and 

 (2) a new exposition of the torsional movements which differs from 

 the book here reviewed as well as from the above-cited article of 

 the reviewer. 



The Torsional Movements. 



The very lucid map of the book showing the tetrahedral de- 

 formation is here reproduced (Fig. i) and the reviewer has added 



