COAL FIELDS. 257 



these beds always contain the well known vegetable fossils, stigmaria. 

 The statement of the fact we owe to him. Its modern significance 

 escaped him for the time. The proof was forthwith furnished by Binney, 

 that the stigmaria are the roots or underground stems of lepidodendroid 

 and sigillaria trees. At about the same time came the discovery, in a 

 railway cutting near Manchester, of a number of sigillaria trees, standing 

 unmistakably where they grew and immediately connected with an over- 

 lying coal seam. These were the initial and epoch-marking facts of the 

 subject, but they have been repeated and supplemented and extended in 

 ever}- region of the world in which coal is mined, from that day to this, 

 until they have become, to the last degree, familiar and commonplace. 



As we advance beyond this position and inquire as o the conditions 

 and modes of growth of this land vegetation, we find ourselves at once 

 among unsettled questions. Most of the well matured and more elabo- 

 rate theories that have been advanced in recent times, however, agree still 

 further, and, in regard to a very important factor in the discussion. Almost 

 all of them hold that this vegetation grew on lowlands, and not only near 

 the sea level but near the sea itself. The obvious facts of almost every 

 section of Carboniferous rocks, in which a seam of coal is included, 

 allow, indeed, no escape from this conclusion, but the particular modes of 

 growth of these great sheets of vegetation are variously conceived and 

 represented. 



(a) Forests growing on swampy tracts, finally submerged and 

 buried under sheets of sand or clay, the forest trees themselves, and 

 chiefly their bark, constituting the bulk of the coal; this is one of the 

 earlier and cruder theories which it is somewhat surprising to find still 

 surviving. It has recently found new expression through Carruthers, 

 the distinguished paleo-botanist, who seems to adopt it without reserve. 

 Several elements of it also enter into the extravagant theory of Grand- 

 Eury which has recently appeared. 



(6) An accumulation of vegetation quite after the manner of the 

 mangrove swamps of sub-tropical lands at the present time makes 

 another theory. Sir Archibald Geikie adopts this as the best picture of 

 the conditions of coal formation that we can find in the existing order of 

 things. 



(c) By Sir Charles Lyell, the cypress swamps of the lower Miss- 

 issippi were made to do like service. Sir William Dawson seems to 

 agree with L,yell that the conditions of coal formation are most adequately 

 represented by these great accumulations. 



(d) Fifty years ago Brogniart made the suggestion in an almost 

 incidental way that we should find in the peat bogs of today the ana- 

 logue and representative of the coals seams of Carboniferous time. It 

 is not necessary to claim that a suggestion of this sort had never been 

 made before, for such a claim could not be maintained, but the time had 



17 G. C. 



