REVIEWS. 527 



The minerals composing these rocks, wherever found, generally agree 

 in showing evidence of extensive dynamic changes, as do also the rela- 

 tions of each sort of rock composing the system, to each other. So 

 closely do the rocks of this system resemble each other in different 

 regions, that Professor Van Hise says that a suite of specimens of 

 Archean rocks from any one of the regions examined by him, if not 

 labeled, "could by no possibility be asserted not to have come from 

 any other." The system is a unit, both in its positive and negative 

 characters. 



To the Archean system thus defined are referred the basement com- 

 plexes of Arizona, of the Wasatch Mountains, of certain ranges of 

 Nevada, of Southwest Montana, of Texas, of the Lake Superior region, 

 of the Hudson Bay region, probably the basement complex of New- 

 foundland, and much of the great area of Northern Canada, known as 

 Laurentian. The basal complexes of the Front range, and of the 

 Quartzite Mountains of Colorado, are referred to the Archean with less 

 confidence. Still other areas not yet definitely classified may prove to 

 be Archean in whole or in part. 



With reference to the origin of the Archean, Professor Van Hise 

 inclines to a modification of the theory that the system represents a 

 part of the original crust of the earth. He believes that the Archean 

 rocks were originally igneous, and that they may include not only such 

 remnants of the pre- sedimentary crust as may exist, but those deeper 

 parts of the crust which became lithified in later times, and which have 

 reached the surface by denudations. He suggests that the banded and 

 contorted granite-gneiss which serves as a background for the Archean 

 may represent the rocks having such an origin, while the other parts of 

 the system may be subsequent eruptives, assignable to no other system, 

 and physically a part of the Archean. 



The author does not overlook the fact that this suggestion con- 

 cerning the origin of the Archean may make the system include rocks 

 which crystallized below the outermost crust after sedimentation began, 

 and that the date of this lithification may therefore be Algonkian, or 

 even post-Algonkian. Their crystallization at such a date is not looked 

 upon as sufficient reason for excluding them from the Archean group. 

 It is manifestly impracticable to have an Algonkian system below the 

 Archean, representing crystallization or lithification synchronous with 

 the Algonkian sedimentation above. 



This being the conception of the Archean, it is evident that strati- 



