230 GEOLOGICAL TIME 



symptoms of growth or of collapse ? Are they accom- 

 panied with even the slightest amount of elevation or 

 depression ? We cannot tell. But these questions are 

 probably susceptible of some more or less definite 

 answer. It might be possible, for instance, to deter- 

 mine with extreme precision the heights above a given 

 datum of various fixed points along such a chain as 

 the Alps, and by a series of minutely accurate measure- 

 ments to detect any upward or downward deviation 

 from these heights. It is quite conceivable that through- 

 out the whole historical period some deviation of this 

 kind has been going on, though so slowly, or by such 

 slight increments at each period of renewal, as to 

 escape ordinary observation. We might thus learn 

 whether, after an Alpine earthquake, an appreciable 

 difference of level is anywhere discoverable, whether 

 the Alps as a great mountain-chain are still growing 

 or are now subsiding, and we might be able to ascer- 

 tain the rate of the movement. Although changes 

 of this nature may have been too slight during human 

 experience to be ordinarily appreciable, their very 

 insignificance seems to me to supply a strong reason 

 why they should be sought for and carefully measured. 

 They would not tell us, indeed, whether a mountain- 

 chain was called into being in one gigantic convulsion, 

 or was raised at wide intervals by successive uplifts, or 

 was slowly elevated by one prolonged and continuous 

 movement. But they might furnish us with sugges- 

 tive information as to the rate at which upheaval or 

 depression of the terrestrial crust is now going on. 



The vexed questions of the origin of Raised Beaches 

 and Sunk Forests might in like manner be elucidated 



