16 STE/ENSON— FORMATION OF COAL BEDS. [April 21. 



plants, bcinj,^ aquatic in t}pc, grew in low moist forests in marshes 

 on the borders of lakes or rivers. From the fact that peat occurs 

 in only limited quantity within the tropics, he argues against the 

 supposed tropical nature of the carboniferous plants. These em- 

 bedded plants are so often in such state of preservation as to pre- 

 clude the notion that they had been transported. MacCulloch's 

 study of peat bogs led him to recognize four types. Marsh deposits 

 are vast in area, uniting on one side with Lake deposits and on the 

 other with Forest deposits, as they may be on either lowland or 

 upland. They owe their origin ch'iehy to Sphagnum pal ust re. Two 

 sets of plants aid in forming the lake deposits ; shallow portions of 

 the lake give floating plants, which, after flowering, sink to form 

 a vegetable stratum ; other plants fringe the pond, detain clay and 

 detritus, supporting reeds and bulrushes ; these gradually advancing 

 form a marsh and eventually the lake is filled. The Forest peat 

 contains submerged wood and is produced, for the most part, by 

 plants after fall of the forest, so that it is a marsh peat. It is 

 always forming in forests and the submerged tree-trunks are almost 

 wholly in one direction, having been overthrown by the wind. ]\Iari- 

 time peat is formed in estuaries by Zostcra iiiariiia. which causes 

 formation of sandbanks and bars ; seaweeds may contribute even to 

 shore peat, for Fiicus scrratits and F. nodosus are found in deep 

 peat at some places in Holland. Transported peat is rare, occurring 

 only in small (juantities and as a fine powder ; it is due to bursting 

 of bogs. AlacCullocli, alter a detailed comparison of phenomena 

 observed in peat bogs with those observed in coal deposits, concluded 

 that by far the larger part of the coal deposits are now lying where 

 the progenitor plants grew. 



jMammatt-'* appears to have been the first to recognize that an 

 underclay usually accom])anies coal beds. " Seams of fireclay abound 

 in the Ashby coal-field and there are very few coal-measures which 

 do not rest upon it, as the sections will show." Jle remarks further: 

 " From the circumstance, that so many cases occur, where a toler- 

 ably pure fireclay lies immediatel}- under, and in contact with, a bed 



"* E. Mnniniatt, "Coal Vidd of Aslihy dc la Zouclic." 1834 p. jt,. Cited 

 by II. 1). Rogers, Assoc. Anier. Geol. and .\at.. Btslon. 1843 [i. 454. 



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