634 



HISTORICAL GEOLOGY. 



channel, in coal-making times, as is proved by the coal-beds in Newfound- 

 land, Nova Scotia, and New Brunswick on the north, and in Khode Island 

 and a part of eastern Massachusetts on the south. 



The "Western Interior, Rocky Mountain, and Pacific Border regions of the 

 continent were largely covered by the Mediterranean Continental Sea, so that 

 the western part of the map for the Upper Silurian era, on page 536, answers 

 sufficiently well for this portion of the continent in the Carbonic era. 



Subdivisions. 



3. Permian Period. 



PENNSTLTANIA. 



The Upper Barren 

 Measures. 



MISSISSIPPI BASIN. 



Permian beds. 



2. Carboniferous 

 Period. 



1. Subcarboniferous 

 Period. 



< 



4. Upper Productive 

 Measures. 



3. Lower Barren Meas- 

 ures. 



2. Lower Productive 

 Measures. 



1. Pottsville Conglom- 

 erate, or Millstone Grit. 



2. Mauch Chunk group 

 of Lesley. Umbral of 

 Rogers. 



1. Pocono group of 

 Lesley. Vespertine of 

 ^ Rogers. 



2. Coal-measures. 



1. Millstone Grit. 



4. Chester, or Kaskas- 

 kia group. 



3. St. Louis group. 



„ ^ r Warsaw. 



- ^'^^' Keokuk. 

 ^''''^- I Burlington. 



1. Kinderhook group. 



The Subcarboniferous rocks of the Mississippi basin are mainly great 

 limestone formations. The term Subcarbomferous was first applied to them 

 by D. D. Owen in his Quarto Report, of 1852, on the Geology of Wisconsin, 

 Iowa, and Minnesota. In this report (page 90) he divides the Carboniferous 

 rocks of Iowa into "(1) the great calcareous formation at the base, (2) the 

 coal-bearing strata in the middle, and (3) heavy beds of sandstone at the top," 

 and gives (on page 92) a section of the " Subcarboniferous limestones." On 

 the following page he presents a "table exhibiting the analogy between the 

 Carboniferous limestones of Yorkshire, England, and those of Iowa," thus 

 applying the term, in effect, to the corresponding rocks of Great Britain and 

 Europe. The preposition sub is here used in the same sense as in substructtire ; 

 and the great limestone formations of the Mississippi basin make a grand 

 substructure for the coal-measures or the beds of the Carboniferous period. 

 The term Mountain limestone, used for the British rocks, and for awhile 

 employed in the United States, is not applicable to limestones of the plains. 



