MAPS AND CLASSIFICATION 515 



were displayed under nearly all their grander types before the close of this 

 section of Paleozoic time; and also that the highest division of the Animal 

 Kingdom, Vertebrates, was represented by species of the inferior type of Fishes. 



"The second of the sections, the Neopaleozoic, was characterized by the grad- 

 ually increasing extent of dry land over the continental area, and the covering 

 of the emerged surface with land plants, and finally with great forests. . . . 



"The Eopaleozoic section was . . . the time of the Reign of the Inverte- 

 brates, and prominently of Trilobites ; the Neopaleozoic, in its Upper Silurian 

 and Devonian eras, the time of the Reign of Fishes, and in the Carbonic era, 

 that of the Reign of Amphibians" (460). 



With Dana it must be agreed that the Taconic revolution is a "critical 

 period," and that in geologic classification it has the value of other critical 

 periods. The writer therefore proposes that the Paleozoic be divided into 

 two independent eras. For the earlier portion, or Dana's Eopaleozoic, it 

 seems wise to return to the original usage of Paleozoic, but modified to 

 agree with present knowledge. Paleozoic will therefore supplant Eopaleo- 

 zoic, while Neopaleozoic will be preserved with the limitations as defined 

 by Dana. 



As to the nomenclature of eras and systems, etcetera, the writer fur- 

 ther proposes to follow the rules adopted by the International Geological 

 Congress in regard to a unification of nomenclature. Geikie 139 has 

 summed up these rules as follows : 



"The International Geological Congress has, since 1881, laboured strenuously 

 to effect some reform in this matter, but only with partial success. The 

 scheme adopted at the last meeting (Paris, 1900) comprised the following 

 stratigraphical subdivisions : 1st Order : Eras of time, represented by Groups 

 of strata, Paleozoic, Mesozoic, Cainozoic. 2nd Order : Periods of time, repre- 

 sented by Systems of strata, as in the four great Paleozoic systems. 3rd 

 Order : Epochs of time, represented by Series of strata. 4th Order : Ages of 

 time, represented by Stages of strata, oth Order : Phases of time, represented 

 by zones of strata. . . . The divisions of the second order are all made to. 

 terminate in ique. ... Or Cambric, Siluric, Devonic, as they would be 

 written in English. The divisions of the fourth order are meant all to end in 

 en (an in English), as Bartonian, Portlandian, etc." 



The eras and periods will be drawn as follows : 



The eras are delimited by the "critical periods" in the earth's history. 

 They are marked by long periods of extensive mountain making and 

 periods of long and decided emergence. The old condition of things is 

 brought to an end, and is followed by a greatly altered physical aspect of 

 the lands and seas. These changes also greatly affect the life of both 

 land and sea, their results being easily discernible in the life of the open- 

 ing periods of the eras, the Paleozoic, the Neopaleozoic, the Mesozoic, and 

 the Tertiary or Neozoic. 



139 Geikie : Text-book of Geology, 2d edition, 1903, p. 859. 



