Ixii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



were accumulated are so countless, as to have afforded ample time 

 for the upheaval of much crystallme 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 se- 

 dimentaiy strata newer than the coal, for some part of the materials 

 of such strata have been more than once ground down 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 ques- 

 tion discussed in this Address. Until the transporting power of gla- 

 ciers and icebergs was better understood, no geological phsenomena 

 were oftener appealed to in support of violent earthquake-waves, 

 sudden deluges, rapid and overwhelming currents of mud, and other 

 extraordinary agencies, than the northern and Alpine erratics scattered 

 over hill and dale, and having no obvious relation in their geogra- 

 phical 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 surface of a glacier, never 

 halting day or night, summer or winter, appears rarely to exceed, 

 according to the exact measurements 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 inap- 

 preciable by human sight. I have seen hundreds of these floatiug 

 bergs at once in the Atlantic on their way southwards ; but no ob- 

 server could determine their direction, or decide whether they were 

 aground or in motion, unless he had opportunities of comparing their 

 relative position from day to day. So large is the volume of ice sub- 

 merged beneath the water, that the waves and swell of the Atlantic 

 during a storm have no more power to communicate a rocking motion 

 to one of them than if they were islands, or parts of the firm land. 



