300 THE BORDERLAND OF SCIENCE. 



with many geologists that the coal-seams were formed 

 of vegetable matter (the rubbish of decayed forests) 

 which had been carried by rivers into estuaries and 

 there formed into vast natural rafts. It was supposed 

 that such rafts, sinking to the bottom, became after a 

 while covered with a layer of sand or mud. The up- 

 rightness of the tree-stumps, however, as compared 

 with the position of the coal-beds that is to say, 

 their position square to these beds should of itself 

 have disposed of the theory referred to. 



Yet, on the other hand, there is great difficulty in 

 understanding under what circumstances the alternate 

 rising and sinking of the level of these delta-swamps, 

 or morasses, took place during the enormously long 

 period of time which must have been occupied in the 

 formation of the carboniferous groups with a thickness 

 amounting in some places to nearly four miles. We 

 see, for instance, that in the case of the Nova Scotia 

 coal-fields, there must have been eighty-one distinct 

 submergences. Now there is nothing remarkable in 

 the mere circumstance that the same part of the earth 

 should have been above and beneath the sea-level 

 through many successive alternations. Geology has 

 long taught that in nearly every part of the earth this 

 must have happened. But that throughout so many 

 as eighty-one such changes those conditions should 

 have been repeated which are necessary for the forma- 

 tion of coal-beds, is indeed a most remarkable circum- 

 stance. We have, on the one hand, the indications of 

 a surprising degree of subterranean activity for, 



