22 ANCIENT PLANTS 



figured in fig. 12 shows how the soft tissues of young- 

 leaves are preserved, and how their relation to each 

 other and to the axis is indicated. 



Hitherto the only concretions of the nature of "coal 

 balls " containing well preserved plant debris, have been 

 found in the coal or immediately above it, and are of 

 Palaeozoic age (see p. 34). Recent exploration, however, 

 has resulted in the discovery of similar concretions of 

 Mesozoic age, from which much may be hoped in the 

 future. Still, at present, it is to the palaeozoic specimens 

 we must turn for nearly all valuable knowledge about 

 ancient plants, and primarily to that form of preservation 

 of the specimens known as structural petrifactions, of 

 which the "coal balls" are both the commonest and the 

 most perfect examples. 



CHAPTER III 



COAL, THE MOST IMPORTANT OF PLANT REMAINS 



Some of the many forms which are taken by fossil 

 plants were shortly described in the last chapter, but 

 the most important of all, namely coal, must now be 

 considered. Of the fossils hitherto mentioned many are 

 difficult to recognize without examining them very 

 closely, and one might say that all have but little 

 influence on human life, for they are of little practical 

 or commercial use, and their scientific value is not yet 

 very widely known. Of all fossil plants, the great ex- 

 ception is coal. Its commercial importance all over the 

 world needs no illustration, and its appearance needs no 

 description for it is in use in nearly every household. 

 Quite apart from its economic importance, coal has a 

 unique place among fossils in the eyes of the scientist, 

 and is of special interest to the palaeontologist. 



In England nearly all the coal lies in rocks of a 



