530 THE JOURNAL OF GEOLOGY. 



to attempt to summarize this discussion, since it is as brief as is con- 

 sistent with adequacy, in its original form. Suffice it to say that while, 

 as applied to Paleozoic rocks, the value of lithological characters and 

 structural relations are well understood, they have a somewhat differ- 

 ent meaning and a greater relative value when applied to the pre- 

 Cambrian formations. At the same time this application is more 

 difficult. 



One of the most valuable parts of the volume consists of the twelve 

 maps, covering most of the areas where pre-Cambrian rocks are known 

 or suspected. Nowhere else does Professor Van Hise succeed better 

 in making the indefiniteness of our knowledge definite, than on the 

 maps. On but two of the twelve maps does he represent Archean 

 rocks, viz., on the maps covering the original Huronian area and its sur- 

 roundings, and on the map of the Lake Superior region. Within the 

 United States, Archean rocks are mapped in but three states — Minne- 

 sota, Wisconsin and Michigan. This does not mean that Archean 

 rocks do not exist elsewhere, or that they are not known elsewhere, 

 but that their areas elsewhere, so far as covered by the maps, have not 

 been defined. Some of the areas which we have been accustomed to 

 see represented as Archean on maps made before the Algonkian was 

 differentiated, are now represented as "unclassified pre-Cambrian." 

 Of this the Adirondack region may serve as an example. The maps 

 tell us only that the rocks of this region may be Algonkian, or Archean, 

 or both. In the text Professor Van Hise's opinion concerning the 

 area may be found. This is to the effect that the Algonkian is cer- 

 tainly represented in the region, and Archean possibly, but that 

 existing knowledge on the .point is not sufficiently definite for carto- 

 graphic representation. Other areas which have been mapped as 

 Archean are represented simply as "unclassified partly or wholly 

 crystalline rocks." Of the areas thus represented, the whole of the 

 crystalline schist belt of the Appalachian region may serve as an exam- 

 ple. The author's map does not even assert that these rocks, or any 

 part of them, are pre-Cambrian. Here again we find the author's 

 opinion in the text, where it is indicated that parts of this area are 

 pre-Cambrian, while other extensive portions may, or may not be. 

 Such pre-Cambrian areas as are known are not defined, and therefore 

 cannot be represented on the maps. 



Algonkian rocks find definite representation in more regions than 

 the Archean. They appear upon the maps in Arizona, New Mexico, 



