President of the Geological Society for 1850. 37 



hour, and these currents might move blocks of great magni- 

 tude from place to place. Thus a current of ten miles an 

 hour would be capable of propelling a block of five tons 

 weight, and its force increasing in the ratio of the square of 

 its velocity, a current of twenty miles an hour would move 

 a block of 320 tons. The experiments of Mr Scott Russell 

 on the velocity of waves of translation, although made with 

 much smaller waves, are supposed to bear out these views.* 

 Now, adopting all the mathematical and hydrostatical cal- 

 culations of Mr Hopkins as correct, they prove, I think, the 

 non-occurrence or extreme rarity in past times of earthquake- 

 shocks more violent than such as we have experienced in the 

 last ten centuries. For when we consider how many marine 

 formations have been upraised, some of them from seas of 

 considerable depth, and what a vast amount of upheaval and 

 subsidence, estimated, as I have already reminded you, by 

 miles vertically, has taken place, it seems clear that if cur- 

 rents and waves of such power as those contemplated by 

 Mr Hopkins had really been set in motion, there would have 

 been erratic blocks in deposits of all ages, instead of their 

 being confined to the close of the tertiary period. Had these 

 mighty waves swept again and again over the floor of the 

 ocean, and over the land in ancient periods, a drift or boulder 

 clay with rounded and angular blocks would have been 

 conspicuous in the Eocene, Cretaceous, Jurassic, Triassic, 

 Permian, Carboniferous, Devonian and Silurian formations, 

 and would have been most strikingly displayed in such of 

 these epochs as have been of the longest duration. I have 

 seen fragments of gneiss eight feet in diameter in the base 

 of the Silurian series in Canada, in the group called by the 

 New York geologists the Potsdam sandstone ;t but I ob- 

 served in the same place similar gneiss in situ, in the im- 

 mediate vicinity, so that the blocks may have been detached 

 from an undermined clifi^ of the Silurian sea-coast. In like 

 manner, in the valley of the Bormida, in Piedmont, there are 

 huge rounded masses of serpentine in the tertiary molasse ; 

 but similar rocks in situ pre-existed in the same region, so 

 that blocks may have been derived from the destruction of 



* Hopkins, Quart. Journ. Geol, Soc. of Lond. vol. iv. p. 70, No. 13. 

 t See Travels in North America, vol. ii. p. 126. 



