A FEW WORDS ABOUT COAL. 297 



material which, had supported the sandstone mass is 

 necessarily removed. Hence the miners look with 

 dread on these coal-pipes, as they are called, which 

 each year cause fatal accidents in the Newcastle and 

 other coal-fields. As Sir Charles Lyell well remarks, 

 6 it is strange to reflect how many thousands of these 

 trees fell originally in their native forests in obedience 

 to the law of gravity, and how the few which continued 

 to stand erect, obeying, after myriads of ages, the same 

 force, are cast down to immolate their human victims.' 

 We see, then, that coal-seams are the remains of 

 ancient vegetable layers, formed underneath the trees 

 of the ancient forest. But it is not to be supposed 

 that every forest in those old times spread its shade 

 over a mass of decaying vegetable matter, until the 

 time should come when the mass should be covered 

 over with shale or sandstone. In order that coal-seams 

 should be formed, it was necessary that the forest 

 region should be so abundantly watered as to form a 

 forest swamp, like the cypress-swamps of the Mississippi. 

 Yet again, it was necessary that during the fresh-water 

 inundations which helped to accumulate the vegetable 

 matter round the roots of the ancient forest-trees, no 

 mud should be carried into the swamps. As Lyell says, 

 * one generation after another of tall trees grew with 

 their roots in mud, and their leaves and prostrate 

 trunks formed layers of vegetable matter, which was 

 afterwards covered with mud, since turned to shale. 

 Yet the coal itself, or altered vegetable matter, 

 remained all the while un soiled by earthy particles. 



