ANNIVERSARY ADDRESS OF THE PRESIDENT. xlvii 



States*,' that a great oscillation of level has taken place in the valley 

 of the Mississippi and its tributaries, by means, first, of a slow down- 

 ward movement, and then of an ascending one, and that the whole 

 was accomplished since the period when the freshwater and land- 

 shells now inhabiting that great valley were already in existence. We 

 ought not therefore to be surprised when we discover sea-beaches in 

 Norway 700 feet high, in which the shells are identical with those 

 now inhabiting the German Ocean ; for we have already seen that the 

 rise of land in Scandinavia, however insensible to the inhabitants, is 

 rapid when compared to the rate of contemporaneous change in the 

 testaceous fauna. Were we to wait therefore until the mollusca shall 

 have undergone as much fluctuation as they underwent between the 

 period of the liassic and upper oohte formations, or still more between 

 the oolite and chalk, or between the Wealden and eocene strata, what 

 stupendous revolutions in physical geography ought we not to expect, 

 and how many mountain-chains might not be produced by the repe- 

 tition of shocks of moderate violence, or by movements not even per- 

 ceptible by man ! I may take this opportunity of stating, in refer- 

 ence to the permanent eifects of subterranean movements in our 

 times, that in all likelihood we are always in danger of underrating 

 their intensity, because we can only measure their amount on the 

 sea-coast, whereas the adjoining mountain-chains seem generally to 

 be more shaken by earthquakes, and probably undergo a greater 

 change of level than the low countries. 



Let us now return to the Alps, and inquire whether geologists who 

 ascribe their origin to paroxysmal forces have been able of late years 

 to bring to light any new facts in support of their favourite doctrine. 

 On the contrary, if I mistake not, they have been more and more 

 compelled to assign the time during which the disturbing power was 

 exerted to a succession of distinct geological periods, in some of 

 which the force must have operated very slowly, while in other cases 

 where it was sudden it may probably have been intermittent, and 

 consisted, as in ordinary volcanic action, of a repetition of shocks or 

 explosions of moderate intensity. In illustration of these principles, 

 I may first mention that some of the volcanic eruptions of the Alps, 

 which produced the porphyry called melaphyre, broke out again and, 

 * Vol. ii. chap, xxxiv, * 



