110 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



the same in composition as the peat from Sumatra and other islands 

 within the tropical regions. The differences in composition of peats 

 from these widely separated localities are little greater than those ob- 

 served in the several benches of any thick deposit. 



5. The felted structure of the peat is not due to any special 

 character of the plants, for it is present in forest litter. The extent 

 of chemical and physical change increases downward in a deposit. 

 At the top of a growing bog, one finds living plants, but within two 

 or three inches, the mass consists of dead material, slightly changed 

 in color but with small increase in percentage of carbon. Lower 

 down, the organic structure becomes less and less distinct and, at 

 length, the whole mass is, to the unaided eye, merely a pulp, in 

 which are embedded fragments of wood and occasional leaves. The 

 condition is described by both Darwin and Thomson for southern 

 latitudes. The former, in writing of Tierra del Fuego, says that 

 Astclia piiinata constantly produces new leaves on the growing stem, 

 while the older ones decay. Traced downward into the peat, the old 

 leaves can be seen in all stages of decomposition until the whole 

 has been blended into a confused mass. Thomson says of the 

 Falkland peat that roots of Empetnim, Myrtus, Caltha and sedges 

 can be traced downward for several feet, but finally all structure is 

 obliterated and the whole is reduced to an amorphous, structureless 

 mass. Examined under a glass, this pulp proves to consist mostly 

 of plant remains, fragmentary and irregular in form. The unequal 

 action of decomposing agencies causes this peculiarity of form, 

 which might suggest to some that the plant remains had been sub- 

 jected to attrition during transport by running water. But the ma- 

 terial is of in situ origin, and all stages of change are distinct. 



The several parts of plants are affected dift'erently and not all 

 plants are aft'ected alike. Hypnum appears to be especially resistant, 

 for layers of the almost unchanged moss have been found under- 

 lying a considerable thickness of pulpy material. The soft parts 

 of plants are reduced quickly and the wood of most deciduous trees 

 is reduced but little less rapidly. The wood of oak and conifers 

 remains unaft'ected for long periods, practically the only apparent 

 change being increase in hardness. The bark of nearly all trees 



