A PIECE OF COAL. 



613 



coal of Iowa was accumuTated in what is called the Carboniferous age 

 an age of the world that is immensely distant from the present, in- 

 finitely so, indeed, as we count time yet the processes of Nature were 

 the same then as now. That old world was, in every essential par- 

 ticular, the same world that we know, and was governed by precisely 

 the same laws that control it to-day. What is true of coal is also true 

 of every pai't of the geological record to this extent : that all the 

 strangely fascinating history recorded in the rocks must be read in the 

 light of what may be seen actually taking place now. It has become 

 a maxim of geology that, if we would know how anything was done 

 in the past, we must study the method in which Nature is doing that 

 very same thing in the present. Following these suggestions a little 

 further, we are led from the study of this particular side of the history 

 of coal, through similar studies, to the grander and more significant 



Fig. 4. Sigillakia reticulata. 



Fig. 5. Sigiixaeia Gr^seri. 



generalization that the laws that govern the world have been the same 

 for all time ; that the laws of matter were imposed upon it as long ago 

 as that old, old nebula of which you have heard, and that there has 

 been no occasion to repeal the old or enact any new laws since. 



But we must get back to our coal, and pursue the series to which 

 it belongs a little further. The product of our Iowa mines is one of 

 the terms, as we have seen, in that interesting series, but it is not the 

 final term. We may start with bituminous coals, like those of Iowa, 

 at Pittsburg, for example, and working our way across the State of 

 Pennsylvania toward the foot-hills of the Alleghanies, we will cross 

 one of the grandest coal-fields in the world, and at every stage of 

 progress will pass from more to less bituminous coal, until by almost 

 imperceptible gradations we will find ourselves in the region of an- 

 thracite. Anthracite, then, is only another term in the coal series ; it 



