FORMATIONS AND PHYSICAL HISTORY 



369 



order of ;i'4r, ;irc shown below, but it cannot be affirmed that any 

 one lit" tin-ill is tin- exact equivalent of any one in New York. 



Upper Ordovieian 5. Hudson River 1 (Maquoketa) shale 



J 4. Cialena limestone 

 Middle Ordovician > T> i- 



( 3. Trenton limestone 



$ 2. St. Peter sandstone 

 Lower ( Jrdovii lan ,, . .. 



( i. Lower Magnesian limestone 



In the mountains of Tennessee, a series of limestone or dolomite 

 beds (Knox, Chickamauga, etc.), is followed by a series of clastic 

 bi-ds i Sexier shale, Bays sandstone, etc.). 2 The exact relations of 

 these formations to those of New York and to those of the upper 

 Mississippi basin are undetermined. The section of Tennessee 

 does not correspond in detail with that of other parts of the Appala- 

 chian belt. 



In the Great Plains, the Ordovician system appears at the sur- 

 face but rarely, though it probably underlies the younger formations. 





]'!. 328. Trenton Falls, Trenton, N. Y. The locality whence the Trenton 



formation derived ils name, (l)arton, U. S. (leol. Surv.) 



1 It is now held by some that a portion, if not all. of the Hudson River (Maquo- 

 keta) shale of I lie Mississippi basin is the equivalent of the Richmond beds farther 

 east. 



'The subdivisions mentioned here are those of the Maynardsville, Tenn., 

 ,.lio U. S. Geol. Surv. 



