INTRODUCTION 13 



•we shall have a very fair idea of the kind of material a 

 coal-ball consists of. 



The question whether coal was formed in situ in 

 the actual forest itself, or from vegetable drift carried 

 by currents to a distance, has been much disputed. 

 The accumulations represented by the nodules in the 

 coal must have been formed within the forest region, 

 for the remains that they contain are penetrated in all 

 directions by the rootlets of the trees which grew 

 there. The roof-nodules, however, contain drifted 

 fragments. 



Coal-balls of this kind are limited to certain horizons, 

 and are by no means of general occurrence, even in 

 the Lancashire and Yorkshire district. Naturally, these 

 stony lumps do not improve the value of the coal, and 

 unfortunately for the palseobotanist, the mines which 

 produce them tend to go out of working. At Shore 

 Littleborough, in Lancashire, however, a mine has 

 recently been reopened by the owner, Mr. W. Sutcliffe, 

 F.G.S., for the sake of the petrifactions in which this 

 locality is peculiarly rich. 



For the purposes of the botanist, the petrified 

 remains showing structure are the most important, and 

 will form the main basis of our work, though it is always 

 necessary to correlate them, as far as possible, with 

 specimens which exhibit the external characters. 



In the classification of recent plants, systematic 

 botanists, so far at least as the Flowering Plants are con- 

 cerned, are accustomed to rely chiefly on the morphology 

 of the reproductive organs, and usually on their more 

 external, as distinguished from their microscopic features. 

 Such characters, however, are often absent in fossil 



