510 GEOLOGY 



Other sections. The classification of New York is not applical >le 

 in detail to the system in other parts of the continent. In Wisconsin, 

 Iowa, and Minnesota, for example, the formations commonly 

 recognized, numbered in the order of age, are as follows: 

 Upper Ordovician 5. Hudson River * (Maquoketa) shale 

 Middle Ordovician ^ 



Lower Ordovician \ 



It can hardly be affirmed that any one of these formations is 

 the exact equivalent of any one in New York. 



In the Appalachian Mountains 2 of Tennessee, a series of lime- 

 stone or dolomite beds (Knox, Chickamauga, etc.), the lowest not 

 distinctly marked off from the Cambrian below, is followed by a 

 series of clastic beds (Sevier shale, Bays sandstone, etc.). 3 The 

 exact relations of these formations to those of New York and to 

 those of the upper Mississippi basin have not been determined, 

 and since the strata between Tennessee and these localities arc 

 concealed for the most part, the relations must remain unknown, 

 except in so far as the fossils may reveal them. The section of 

 Tennessee does not correspond in details, with that of other parts 

 of the Appalachian belt. 



General conditions in the eastern part of the continent. It is 

 worthy of note that in mid-Ordovician time, limestone was forming 

 from New England on the east, to Georgian Bay on the northwest, 

 to Oklahoma and Texas on the southwest, and Alabama on the 

 south. Limestone was forming also in much of the west. At no 

 previous epoch was there anything like such wide-spread deposition 

 of limestone within the limits of our continent. The explanation of 

 this condition of things has been suggested already (p. 508). It 



1 It is now held by some that a portion at least of the Hudson River shale 

 of the Mississippi basin (Maquoketa of Iowa, Illinois, etc.) is the equivalent 

 of the Richmond beds farther east. Its classification with the Ordovician 

 is therefore subject to question. (See footnote, p. 508). 



2 For local details in the Appalachians, see the folios of the U. S. (i-ol. 

 Surv. On the maps of the folios, the Ordovician is classed with the Silurian 

 under the latter name. The text of the folios frequently distinguishes be- 

 tween the Lower Silurian (Ordovician) and the Upper Silurian (Silurian). 



3 The subdivisions mentioned here are those of the Maynanlsville, Term., 

 folio, U. S. Geol. Surv. 



