462 



HISTORICAL GEOLOGY. 



over the Atlantic, because the western half of the continent is so generally 

 covered with Mesozoic and Cenozoic rocks. 



Paleozoic rocks are the prevailing kinds exposed to view over the eastern 

 half of the North American continent, excepting along the borders of the Mex- 

 ican Gulf and of the Atlantic south of New York. The older formations of 

 the series, as the map on page 412 illustrates, lie near the Archaean area, not 

 far north or south of the northern boundary of the United States ; and the 

 newer formations outcrop in succession southward, the Carboniferous covering 

 much of Pennsylvania and other States. 



Fig. 504 is an ideal section of the Paleozoic rocks of New York, along a 

 line running southivesttvard from the Archaean across the state to the coal 



504. 



Carbonic. 



Devonian. 



Upper Silurian. Lower Sil. Camb. 



region of Pennsylvania. It shows the relative positions of the successive 

 strata, — bringing out to view the fact that the areas over the region are only 

 the outcrops of the successive formations. This is all the section is intended 

 to teach ; for the uniformity of dip and its amount are very much exagger- 

 ated, and the relative thickness is disregarded. Along the Appalachians the 

 older Paleozoic rocks occur in long belts parallel with the axis of the range, 

 because of the great upturning of the formations that took place at the close 

 of the Carboniferous, when the mountains were made. 



EOPALEOZOIC SECTION. 

 CAMBRIAN ERA. 



Stn. — Cambrian, Sedgwick, Bep. Brit. Assoc, 1835. Cambrian (Murchison's Lower 

 and Upper Silurian being made higher divisions of the Paleozoic series), Sedgwick, 

 Q. J. G. Soc, 1846, page 130. Cambrian (Murchison's Lower Silurian being included 

 under it), Sedgwick, Q. J. G. Soc, 1852, page 147. Lower part of Lower Silurian, Mur- 

 chison, Q. J. G. Soc, 1852, page 173; D'Orbigny, Geol, 1851. 



Cambrian, Lyell, Elements Geol., 2d ed., 1841 ; 5th ed., 1855; Geikie, Text-book of 

 Geol., 1879, 1885 ; Lapparent, Tr. de Geol., 1883 ; Seeley and Etheridge, Man. Geol., 

 1885 ; Prestwich, Geol, 1886 ; E. Kayser, Lehrb. geol. Form., 1891. 



Primordial or lower division of the Silurian System, Stage C, Barrande, Syst. Silurien 

 de Boheme, 1852. Cambrian or Primordial, a subdivision of the Lower Silurian, this 

 Geol, 1874, 1880; C. Vogt, Geol, 2d ed., 1866; Credner, Geol, 6th ed., 1887. 



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