MAPS AND CLASSIFICATION 513 



increasing loads a further explanation why the oceanic areas are in gen- 

 eral constantly subsiding ? 



Desceiption of the paleogeographic Maps and Classification of 

 the American geologic Formations into Periods and Eras 



paleozoic and neopaleozoic 



Before defining the term Paleozoic, it will first be necessary to call 

 attention to the nomenclature of the earlier era or eon, the Proterozoic, 

 which is interpreted by Chamber lin and Salisbury (II : 162) thus : 



"To the Proterozoic era is assigned the time . . . between the close of 

 the Archean and the beginning of the Paleozoic." "Proterozoic, as here used, 

 is a synonym for Algonkian as used by the U. S. Geological Survey." 



The question that now arises is, Does the nearly forgotten term Proto- 

 zoic of Sedgwick 137 cover the same ground ? The original definition is as 

 follows : 



"Class I — Primary stratified groups 



"Gneiss, mica slate, etcetera, Highlands of Scotland and the Hebrides. 

 Crystalline slates of Anglesea and the S. W. coast of Carnarvonshire. 



"The series generally without organic remains ; but should organic remains 

 appear unequivocally in any parts of this class, they may be described as the 

 Protozoic system. 



"Class I ( a). The crystalline slates of central Skiddaw forest, and the upper 

 Skiddaw slate series. The whole is inorganic and intermediate between Class 

 I and Class II." 



In the following year Murchison 138 proposed the same word, as follows : 



"But the Silurian, though ancient, are not, as before stated, the most ancient 

 fossiliferous strata. They are in truth but the upper portion of a succession 

 of early deposits which it may hereafter be found necessary to describe under 

 one comprehensive name. For this purpose I venture to suggest the term 

 Protozoic Rocks, thereby to imply the first or lowest formations in which ani- 

 mals or vegetables appear." 



A better conclusion may be reached as to the idea which these geologists 

 intended to convey by also quoting the words used by Sedgwick when he 

 proposed the term "Paleozoic." He states : 



"Class II, or Paleozoic series 



"This class includes all the groups of formations between Class I and the 

 old red sandstone ; and is subdivided as follows : 



"1. Lower Cambrian system. — All the Welsh series under the Bala limestone. 

 The two great groups of green roofing slate and porphyry on the north and 



137 Sedgwick : Proceedings of the Geological Society of London, vol. 2, 1838, p. 684. 

 133 Murchison : The Silurian system, vol. 1, 1839, p. 11. 



