A PIECE OF COAL. 615 



But how are the great ledges of rock above the coal to be ex- 

 plained ? Let us see. The rocks in question are very often sandstone, 

 and if we examine them carefully we find that they are spread out iu 

 layers, that they contain the remains of many marine animals, and that 

 the surface of a very large number of the layers shows signs of having 

 been washed by waves. With the exception that they are somewhat 

 harder and the organic remains belong to more old-fashioned types, 

 these rocks are exact duplicates of the widely spread layers of sand 

 that the ocean is piling along all our shores to-day, and contain the 

 clearest evidence that they have been swept into place by the waves 

 of some old sea. But how came the coal beneath the sea ? That is 

 an important question, and the full answer to it would show that no 

 truth is more plainly taught by all the records of the past and present 

 than that the earth's surface is a very uncertain and unstable affair. 

 You will find your answer to the question on the shores of Greenland, 

 where the coast, for hundreds of miles, is 

 slowly sinking into the sea ; the result in his- 

 torical times being sufficient to convert old 

 marshes into shallow bays over which sands 

 are swept by each returning tide. You will 

 find your answer along the coast of New Jer- 

 sey, in the buried forests with their prostrate 

 trees and upright stumps, all carried down 

 in very recent times by the subsiding land 

 just within reach of the sea. You will find 

 your answer in the buried forests of the delta 

 of the Mississippi. You will find the same 



, - - , , -r Fig. 7. Stigmaria ficoides. 



answer m a hundred other places. Large 



areas of land in different parts of the world are gradually subsiding, 

 and large areas in the Carboniferous age sank down in the same way. 

 Each coal-seam is the record of peat-bog and forest ; the overlying 

 rocks record a period of submergence. 



But the movements in the earth's surface at present are not all 

 downward ; there are, perhaps, as many cases in which the land is ris- 

 ing. During the Carboniferous age, the same thing was true, and it 

 often happened that the area that was carried beneath the sea was, in 

 time, reelevated, and became the platform on which other forests and 

 peat-bogs renewed the work of coal-making. Thus it is that in many 

 coal-fields we find a number of seams, one above the other, and thus it 

 is that we have registered in the coal-beds of Nova Scotia not less than 

 seventy-six distinct upward and downward movements of the surface. 

 The sinking of the old marsh beneath the sea might seem to involve 

 the loss of all the materials that had 'been accumulating during periods, 

 perhaps, for which years would furnish no adequate unit of measure, 

 and yet this very movement was essential to the preservation of the 

 great magazines of energy on which human progress so much depends. 



