President of the Geological Society for 1850. 35 



would then have been unformed, or at least invisible. The 

 ages which have elapsed since the coal-measures were accu- 

 mulated are so countless, as to have afforded ample time for 

 the upheaval of much crystalline rock and metallic ores from 

 great depths, and for the clearing away of superficial matter 

 by aqueous denudation. To what an extent this subsequent 

 denudation has been carried may be shown by adverting to 

 the fact, that the masses removed must have more than 

 equalled in volume all the sedimentary strata newer than the 

 coal, for some part of the materials of such strata have been 

 more than once ground do\Vn into sand or mud since that 

 period and re- stratified. 



Before concluding, I shall say a few words on another 

 very different topic, yet one which has a distinct bearing on 

 the theoretical question discussed in this Address. Until 

 the transporting power of glaciers and icebergs was better 

 understood, no geological phenomena were oftener appealed 

 to in support of violent earthquake-waves, sudden deluges, 

 rapid and overwhelming currents of mud, and other extraor- 

 dinary agencies, than the northern and Alpine erratics scat- 

 tered over hill and dale, and having no obvious relation in 

 their geographical distribution to the present drainage or 

 physical outline of the countries where they abound. The 

 hypothesis which has recently gained more and more favour, 

 as best explaining the dispersion of such blocks, dispenses 

 with all sudden and paroxysmal exertion of force ; nay, 

 more, it does not even call into play a succession of waves 

 such as ordinary earthquakes can produce. The rate at 

 which huge blocks of stone travel for centuries on the sur- 

 face of a glacier, never halting day or night, summer or 

 winter, appears rarely to exceed, according to the exact 

 measurement of Professor James Forbes, half an inch per 

 hour. When the icy mass, with its moraine and included 

 boulders, reaches the sea, and becoming detached on the 

 coast, gives birth to an iceberg, the frozen raft traverses 

 wide spaces of the ocean at the rate of a few miles a day, so 

 that its advance is usually inappreciable by human sight. 

 I have seen hundreds of these floating bergs at once in the 

 Atlantic on their way southwards ; but no observer could 

 determine their direction, or decide whether they were 



