454 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



The Blount Mountain synclinal lobe, southwest of the Gadsden quadrangle, appears to be 

 intermediate to the Warrior field. The stratigraphy as described by A. M. Gibson presents an 

 enlarged number of divisions which show a marked expansion, notably in the lower Pottsville. 

 Though not paleontologically correlated, they appear to be stratigraphicaUy referable to the 

 divisions in the Warrior basin next beyond. 



In the Warrior field the downward pitch of the synclines on passing from the Plateau 

 (northern) district permits the retention of a great thickness, over 3,000 feet, of strata. At the 

 same time the divisions, particularly the lower Pottsville, appear greatly thickened. In McCal- 

 ley's detailed studies of this field ^^^ the individual coals have been traced with great success 

 over the greater portion of the. area. In the following summary of the divisions of this field the 

 sections above the lowest important coal, the Black Creek coal, are given (in averages) for the 

 eastern border of the field, the Warrior River section, and the edge of the Cretaceous overlap on 

 the west. The series below the Black Creek coal is continued by McCalley's average section for 

 Jefferson County,^" which is placed in the middle column. 



TMcJcness, in feet, of Pottsville strata in the Warrior basin region of A abama. 



Eastern 

 border. 



Along 

 Warrior 

 Eiver. 



Western 



border of 



exposed 



"Coal 



Measures." 



9 



10 

 11 

 12 

 13 



14 



15. 



1. Interval of shales, conglomerates, and sandstones 



2. Brookwood coal group; five coals 



3. Interval of shales and sandstones 



4. Gwinn coal group; two coals 



5. Interval of shales, sandstones, and conglomerates 



6. Cobb coal group; three coals 



7. Interval of shales, sandstones, and local thin limestones 



8. Pratt coal group; five coals 



Interval of shales, sandstones, and conglomerates 



Horse Creek (Mary Lee) coal group; five coals 



Interval of shales, sandstones, conglomerates, and local limestones 



Black Creek coal group; three coals 



Interval of shales, sandstones, local limestones, and ten coals, from Black 



Creek coal to top of "upper conglomerate " of Tennessee 



Interval of sandstones, conglomerates, shales, and coals, from top of "upper 

 conglomerate " of Tennessee to top of "lower conglomerate " of Tennessee. 



Interval of conglomerates, shales, and coals, from top of "lower con- 

 glomerate " ("Millstone grit ") to Mississippian 



50 

 125 

 180 



38 

 175 

 170 

 116 

 160 

 340 

 134 

 100 



70 



150 



108 



250 



32 



160 



136 



170 



166 



260 



148 



68 



85 



1,243 



100 



90 



25 

 100 

 125 



23 

 125 



67 

 210 

 140 

 210 

 106 



63 



56 



According to the preliminary correlations by the writer, based on the incomplete study of 

 the Pottsville floras, the sandstones of the Lookout become greatly broken up and parted, with 

 expanded intervals of varying materials, while at the same time earlier beds of lower Pottsville 

 age are assumed to underlie those in contact with the Mississippian at the Tennessee line. He 

 correlates the entire lower part of the section, including the conglomerate and sandstone interval 

 (No. 11) above the Black Creek coal group (the whole averaging about 1,575 feet), with the 

 Ijookout. The Horse Creek coal group and its overlying conglomerate series, making when 

 added to the other about 1,900 feet, is provisionally placed, on the fossil plant evidence, in the 

 lower Pottsville, No. 9 of the section being tentatively correlated with the Raleigh sandstone of 

 the central Appalachian sections. The Horse Creek coal group (Mary Lee) and No. 9, taken 

 together, may be found to represent the recognized difference between the top of the Lookout 

 on the east side of the Tennessee strip and the top of the Lee farther north. 



The Pratt and Cobb coal groups are middle Pottsville, in which the Gwin also belongs, 

 making a total of about 670 feet, and a part of No. 2 should probably also be included. It is 

 thought, however, that the study of the Brookwood (No. 2) plants may show them to be of 

 upper Pottsville age. 



The Cahaba coal field, a few miles east of the Warrior field, occupies a deep-set and com- 

 pound syncline about 40 miles long and 3 to 6 miles in width. A part of its western margin is 

 overturned, and older Paleozoic rocks are thrust on the coals along the eastern border. This 



