HOMOTAXIAL EQUIVALENTS OF THE PERMIAN 337 



rock terranes is likewise genetic. It is strictly a function of 

 cause and effect. It .is only regarding the position of any par- 

 ticular component in a classification, that is subject to a differ- 

 ence of individual judgment. The taxonomic rank of a group 

 may be subject to change as knowledge increases. Among 

 organisms an advancement in rank is frequent. Families event- 

 ually attain the rank of orders; genera of families; smaller 

 groups are classed as genera. The same is true of geological 

 formations. 



Recognizing, in the taxonomy of rock terranes, the five 

 taxonomic ranks of group or assemblage, system, series, stage, 

 and zone, as amply sufficient subdivisions, at least for all prac- 

 tical purposes, a succession of beds at first given only the rank 

 of a stage may be subsequently advantageously raised to that 

 of series. Stage is a local unit ; while series is a provincial one ; 

 and system essentially universal. 



In applying these principles to the Permian, the question 

 resolves itself into two distinct phases : What should be con- 

 sidered the taxonomic rank of the original Permian? and What 

 is the rank of the succession of beds in this country, referred to 

 the Permian ? 



Taxojiomic position of the Original Permian. — Regarding the 

 rank of the so-called Permian in general, there is much differ- 

 ence of opinion. The older school of geologists, that is per- 

 meated thoroughly with the idea that fossil faunas are exactly 

 recognizable the world around, and that we can by them and 

 without effort synchronize the provincial rock successions of 

 different continents, is inclined to recognize in the Permian a 

 universal extension, and to assign it a rank of a system, com- 

 parable to Carboniferous or Devonian. The more modern 

 school of geological investigators, that tests classification and 

 correlation by more that a single standard and that is seek- 

 ing exact results and genetic relationships, would consider the 

 original Permian as a provincial succession, and give it the rank 

 of a series, under the more comprehensive system of the Car- 

 boniferous. 



