i8 ANCIENT PLANTS 



trunks are weathered out and stand together much as 

 they must have stood when alive; they are of course 

 bereft of their foHage branches. 



Such specimens, however, are usually only isolated 

 blocks of wood, often fragments from large stumps 

 which show nothing but the rings of late-formed wood. 

 It is impossible to connect them with the impressions 

 of leaves or fruits in most cases, so that of the plants 

 they represent we know only the anatomical structure 

 of the secondary wood and nothing of the foliage or 

 general appearance of the plant as a whole. Hence 

 these specimens also give a very partial representation 

 of the plants to which they belonged. 



Fortunately, however, there is still another type of 

 preservation of fossils, a type more perfect than any 

 of the others and sometimes combining the advantages 

 of all of them. This is the special type of petrifaction 

 which includes, not a single piece of wood, but a whole 

 mass of vegetation consisting of fragments of stems, 

 roots, leaves, and even seeds, sometimes all together. 

 These petrifactions are those of masses of forest d6bris 

 which were lying as they dropped from the trees, or had 

 drifted together as such fragments do. The plant tissues 

 in such masses are preserved so that the most delicate 

 soft tissue cells are perfect, and in many cases the 

 sections are so distinct that one might well be deluded 

 into the belief that it is a living plant at which one 

 looks. 



Very important and well-known specimens have been 

 found in France and described by the French palso- 

 botanists. As a rule these specimens are preserved in 

 silica, and are found now in irregular masses of the 

 nature of chert. Of still greater importance, however, 

 owing pardy to their greater abundance and pardy to 

 the quantity of scientific work that has been done on 

 them, are the masses of stone found in the English coal 

 seams and commonly called " coal balls ". 



The "coal balls" are best known from Lancashire 



