THE CARBONIFEROUS PERIODS 



473 



brackish water swamps in which were accumu 

 beds of the Carboniferous. When the sinking 

 accumulation of the vegetable matter, for many 

 years, deposits of peat ioo or more feet in thick- 

 ness were sometimes accumulated. These when 

 compressed to coal formed workable coal beds. 

 The accumulation of coal began in the Lower 

 Pennsylvanian (Pottsville), but it was in the 

 upper half of the period that its formation took 

 place on a large scale. 



While coal was accumulating in large quan- 

 tities (never perhaps more than per two cent, of 

 the total thickness of the deposit (Fig. 449) in 

 any one place) in Pennsylvania, West Virginia, 

 Ohio, Tennessee, Illinois, and Iowa, marine 

 conditions prevailed in the west and southwest, 

 and limestones and shales were deposited with 

 no coal. The red Pennsylvanian sandstone of 

 South Dakota and the red conglomerate of 

 Colorado Were probably deposited on land by 

 streams in an arid climate. Marine sediments 

 to a depth of several thousand feet were de- 

 posited over the site of the Sierra Nevada 

 Mountains. 



The thickness of the Pennsylvanian system 

 varies from 4000 to 5000 feet in the Appa- 

 lachians, to 1000 feet in Kansas and Nebraska. 

 In Texas it is said to be 5000 feet thick and in 

 Nevada about 10,000 feet thick. The probable 

 distribution of the seas and swamps of portions 

 of the Pennsylvanian is shown in the accom- 

 panying map (Fig. 448). 



lated the great coal 

 kept pace with the 

















COAL 





V CLAY 

 SANDSTONE 



S^^i 



COAL BED 



H;lay 



i§i 



SANDSTONE 



AND 

 CONGLOMERATE 



BES 





=^7-==^ 



SHALE 



AND 

 SANDSTONE 







^^ 



CONCEALED 

 IMPURE COAL 



SANDSTONE 



£=zr==3 



SHALE 



COAL 



SANDSTONE 



COAL 



SANDY SHALE 



COAL 

 COAL 

 SANDY SHALE 





_ 



B 



-_''~^~- 



^^= 



COAL 



~— - - 



^CLAY 



SANDY SHALE 

 COAL 



==2^ 



Fig. 449. — Section 

 of coal-bearing strata in 

 Pennsylvania, showing 

 the relative amount of 

 coal and barren rock in 

 a rich field. 



Coal Fields of North America 



Productive Coal Fields. — (1) Eastern Canadian and New Eng- 

 land Fields. — Important coal deposits occur in Nova Scotia and New 

 Brunswick on both sides of the Bay of Fundy. Metamorphic coal 

 is also found in Rhode Island, but it is so graphitic as to be of little 

 value at present. 



