446 EMERSON— RECURRENT TETRAHEDRAL DEFORMATIONS. 



paleontological chapters which give the first appearance and duration 

 of each of the large groups of plants and animals. In these tables 

 the part of the earth's history before the beginning of life is assumed 

 to be to the part since as 5 to 3. 



The second or geological section of the book begins with a con- 

 densed systematic discussion of the geological data for the deter- 

 mination of the outlines of the former continents and a comparison 

 of these data with those derived from the distribution of animals. 



These sections take up the larger part of the volume and then 

 four short chapters on Ice periods ; times of volcanic activity ; moun- 

 tain formation, and transgressions prepare for the central idea of 

 the book, viz. : the statement in tabular form of the cycles of the 

 evolution of the earth as given below and the explanation of the 

 same as due to a succession of tetrahedral deformations, producing 

 broad elevated continents and small oceans ; and spherical recoveries, 

 causing broad transgressions of the ocean with low lands. 



To his table of the geological cycles here presented I have added 

 the statements regarding the changing carbonic acid content in the 

 air, and the changes in climate and evolution, drawn largely from 

 the papers of Chamberlin which are cited below. 



The author accepts the tetrahedral deformation of the earth as 

 the basis of the explanation of these cycles. 



The law of least action, he explains, demands that the somewhat 

 rigid crustal portion of the earth keep in contact with the lessening 

 interior with the least possible readjustment of its surface. As a 

 tube collapses into a triangular prism a shrinking sphere tends by 

 the law of least action to collapse into a tetrahedron, or a tetra- 

 hedroid, a sphere marked by four equal and equidistant triangular 

 projections ; and the earth with its three about equal and equidistant 

 double continental masses triangular southward with three intervening 

 depressed oceans triangular northward, its northern ocean and south- 

 ern continent, with land everywhere antipodal to water, realizes the 

 tetrahedroid status remarkably. When repeatedly in former geo- 

 logical ages ocean waters separated Europe and Asia, the agreement 

 with hypothesis was still more marked. Gravity observations and 

 geodetic measurements agree therewith, even giving for Asia a 

 larger tetrahedroid surface than for Europe, and many other geo- 

 logical homologies point in the same direction. 



