]79 



CHAPTER XII. 



THE CARBONIFEROUS fiYHTEM—Continved. 



CUMBERLAND COAL-FIELD, continued — EXPLANATION OF JOGGINS 

 SECTION ANIMAL REMAINS OF THE COAL MEASURES. 



Explanatory Remarks on the Joe/gins Section. 



In tlie section in the preceding chapter the reader will observe the 

 words " Underclay, Stigmaria" frequently recurring ; and over nearly 

 every underclay is a seam of coal. An underclay is technically 

 the bed of clay which underlies a coal-seam ; but it has now become 

 a general term for 2^ fossil soil, or a bed which once formed a terrestrial 

 surface, and supported trees and other plants ; because we generally 

 find these coal uuderclays, like the subsoils of many modern peat-bogs, 

 to contain roots and trunks of trees which aided in the accumulation 

 of the vegetable matter of the coal. The underclays in question are 

 accordingly penetrated by innumerable long rootlets, now in a coaly 

 state, but retaining enough of their form to enable us to recognise 

 them as belonging to a peculiar root, the Stigmaria, of very fre- 

 quent occurrence in the coal measures, and at one time supposed to 

 have been a swamp plant of anomalous form, but now known to have 

 belonged to an equally singular tree, the Sigillaria, found in the 

 same deposits (Fig. 30). The Stigmaria has derived its name from 

 the regularly aiTanged pits or spots left by its rootlets, which proceeded 

 from it on all sides. The Sigillaria has been named from the rows of 

 leaf-scars Avhich extend up its trunk, Avhich in some species is curiously 

 ribbed or fluted. One of the most remarkable peculiarities of the 

 stigmaria- rooted trees was the very regular arrangement of their roots, 

 which are four at their departure from the trunk, and divide at equal 

 distances successively into eight, sixteen, and thirty-two branches, 

 each giving off, on all sides, an immense number of rootlets, stretching 

 into the beds around, in a manner which shows that these must have 

 been soft sand and mud at the time when these roots and rootlets 

 spread through them. 



It is evident tliat when we find a bed of clay now hardened into 



