548 GEOLOGY 



(3) The Northern Interior field, 1 which is confined to the southern 

 peninsula of Michigan and covers an area of about 11 ; 000 square miles. 

 The strata of this field appear to dip gently toward the center of the 

 basin (i.e. toward the center of the Lower Peninsula), but the field 

 is so heavily covered with glacial drift that its structure is less well 

 known than that of the other fields. The formations of this basin 

 were probably never connected with those of the other coal-fields. 



(4) 'The Eastern Interior field 2 covers an area of about 58,000 square 

 miles in Indiana, Illinois, and Kentucky (Fig. 241). About 55 per 

 cent of! the area is productive. About its borders, the beds of the 

 series Are gently inclined, generally toward the center, while in the 

 central part they are nearly horizontal. This field is set off from the 

 Appalachian field on the east, and from the Western Interior field 

 on the west, by broad low anticlines from which the Coal Measures, 

 if ever present, have been eroded, j The former connection of this field 

 with tl^at to the west is probable. 



(5) j The Western Interior and Southwestern fields 3 constitute a nearly 

 continuous area of Coal Measures formations, stretching from northern 

 iSwa to central Texas, a distance of 800 miles, and covering an area 

 of 94,000 square miles, including parts of Iowa, Nebraska, Missouri, 

 Kansas, Arkansas, Indian Territory, and Texas. On the east this 

 field is limited by the broad low anticline which borders the Eastern 

 Interior field on the west. On the west the field is limited by the 

 overlap of younger formations. Except in Arkansas and Indian 

 Territory, where the strata are folded, the beds of the Coal Measures 

 of this area are essentially horizontal. 



(6) The Nova Scotian-New Brunswick coal-field. — This lies on both 

 sides of the Bay of Fundy and contains an area estimated at about 

 18,000 square miles. There are numerous beds of coal several of 

 which are workable. The coal is bituminous and of good quality. 



While the Pennsylvanian system was perhaps less widespread than 

 the Mississippian, in the Mississippi basin, the less extensive system 

 sometimes overlaps the more extensive, as shown on the map (p. 218), 



1 Lane, 22d Ann. Rept. U. S. Geol. Surv., Pt. Ill, pp. 313-331, and Repts. of the 

 Geol. Surv. of Michigan. 



2 Ibid., Ashley, pp. 271-305, and Repts. of the Geol. Survs. of Indiana, Illinois, 

 and Kentucky. 



3 Ibid., Bain and Taff, pp. 335-413. Also State Geol. Surv. Repts. of Iowa, Missouri, 

 Kansas, -Nebraska, Arkansas, and Texas. 



