512 PRINCIPLES OF STRATIGRAPHY 



Comparison with modern moors leads to the conclusion that 

 those of Carbonic time were of the flat or low moor variety, or 

 that type in wliich arboreal vegetation plays a more significant part 

 than it does in our upland bogs. While the seashore or marsh type 

 was not unrepresented, it is apparent from the character of the 

 vegetation that the prevailing moor type of that period, now repre- 

 sented by our coal beds, was of the fresh-water swamp or morass 

 type. The character of the vegetation itself points to this, since 

 the tissues of the Carbonic trees are of coarse-cell type like those 

 of the rapid-growing trees of our swamps, instead of the close- 

 celled type characteristic of upland bogs and due to slower growth. 

 Of all the known modern swamps that of Sumatra, above de- 

 scribed, comes nearest to representing the conditions of the Car- 

 bonic moors, for the character of the vegetation seems to point un- 

 mistakably to a moist, tropical climate for at least part of our Car- 

 bonic coal deposits. 



The place of the modern bulrushes and other reeds was taken 

 in Carljonic time by the gigantic reed-like relatives of the modern 

 Equisetum, i. c, the Calamites. The usual occurrence of these 

 plants in sandstones preceding coal beds indicates that they per- 

 formed much the same land-forming office in those days that the 

 reeds do to-day. They have in common with them the characteris- 

 tic power of sectional repetition of parts which enables the plant 

 to continue growth and putting forth of roots, even though it is 

 progressively buried by the accumulating silt. 



The tree types succeeding the calamites, the Lepidophytes, in- 

 cluding Lepidodendra and Sigillaria, were true swamp plants with 

 horizontally spreading roots, the Stigmaria. These fossil roots have 

 a remarkable similarity to the spreading roots of Pinus and other 

 moor trees of the present day, and, like these, were adapted for 

 growth on wet ground, where firmness of foundation was secured 

 by great horizontal spreading, and where it was not necessary to 

 penetrate into the soil for moisture, as in regions of low-lying 

 ground-water level. A basal enlargement of the trunks of trees, 

 such as characterizes Nyssa uniflora and others of our swamp trees, 

 is also often seen in these Carbonic types. This feature likewise 

 tends to keep the tree erect, owing to the greater weight of the 

 basal portion. Structures suggestive of the cypress knees or pneu- 

 matophores of our subtropical swamps have also been found asso- 

 ciated with the Sigillaria, while structures suggestive of the breath- 

 ing pores or lenticels, so characteristic of the basal portions of the 

 trunks of trees in the tropical swamps, occur in the Carbonic 

 Lepidophytes, where they fofm the Syringodendron surface. 



