V ON THE FORMATION OF COAL 155 



In the first place, the great phantom of geo- 

 logical time rises before the student of this, as of 

 all other, fragments of the history of our earth 

 springing irrepressibly out of the facts, like the 

 Djin from the jar which the fishermen so incau- 

 tiously opened ; and like the Djin again, being 

 vaporous, shifting, and indefinable, but unmis- 

 takably gigantic. However modest the bases of 

 one's calculation may be, the minimum of time 

 assignable to the coal period remains something 

 stupendous. 



Principal Dawson is the last person likely 

 to be guilty of exaggeration in this matter, and 

 it will be well to consider what he has to say 

 about it : 



. " The rate of accumulation of coal was very slow. The 

 climate of the period, in the northern temperate zone, was of 

 such a character that the true conifers show rings of growth, 

 not larger, nor much less distinct, than those of many of their 

 modern congeners. The Sigillaricr, and Calamites were not, as 

 often supposed, composed wholly, or even principally, of lax 

 and soft tissues, or necessarily short-lived. The former had, it 

 is true, a very thick inner bark ; but their dense woody axis, 

 their thick and nearly imperishable outer bark, and their scanty 

 and rigid foliage, would indicate no very rapid growth or decay, 

 In the case of the Sigillarice, the variations in the leaf-scars in 

 different parts of the trunk, the intercalation of new ridges at 

 the surface representing that of new woody wedges in the axis, 

 the transverse marks left by the stages of upward growth, all 

 indicate that several years must have been required for the 

 growth of stems of moderate size. The enormous roots of these 

 trees, and the condition of the coal-swamps, must have exempted 

 them from the danger of being overthrown by violence. They 



