72 GEOLOGICAL SURVEY OF ALABAMA. 



' The Holt Seam carries about 4 feet of coal and nearly 2 

 feet of black band, but with an aggregate of over 5 feet of 

 foreign matter. This foreign matter, clay, slate and rock, 

 were probably local inflows of sediment during its formation, 

 and hence not co-extensive with the seam. It is from this 

 cause that partings in coal seams are produced, and they 

 are for the same reason subject to great and frequent vari- 

 ations in thickness, often terminating altogether. 



This Holt or Big Seam is probably the equivalent or coun- 

 terpart of the "MAMMOTH SEAM" of the Cahaba f Joal Field, 

 which shows unusual variations in its splits and partings. 

 Both occupy about the same position in the coal measures, 

 both are about the same size, over 12 feet from roof to under 

 clay, both have rocky parting near the middle. The Mam- 

 moth Seam splits into two seams toward the south, may not 

 this also split toward the northwest? Or may not the part- 

 ings diminish in that direction and all but one disappear as 

 it is in the Cowden Seam? These querries can only be an- 

 swered satisfactorily by future extensive explorations and 

 practical mining operations. 



A coal mine is now being opened on this seam in S. 4, T. 

 14, R. 1 E., near the bank of the Blackburn Fork, about one- 

 fourth of a mile above the railroad bridge, which, in its pro- 

 gress, may throw additional light on the relations of this 

 very interesting seam of coal. At this opening its position 

 is about 15 feet above the bed of the river, with a dip of 3 

 deg. to the southeast ; this dip in one-fourth of a mile will 

 put it below the bed of the river which here flows northwest 

 with a fall of 10 to 15 feet to the mile. The tunnelling of 

 this seam for any considerable distance will afford data for 

 calculating its range, dip and southeastern outcrop. 



The seam known in the Cahaba Coal Field as the Brock 

 Seam, lying just above the first or Loiver Conglomerate, has 

 not been opened or cut anywhere in this coal field, yet its 

 existence is plainly indicated at many places by fossil coal 

 plant impressions in the rocks at this horizon. And it was 

 seen, and had been dug into, yet farther to the east, near 



