RATE OF CRUST MOVEMENTS 39 



sandstone which contribute so largely to some of our 

 ancient systems, such as the Cambrian, Old Ked Sand- 

 stone, Millstone Grit, and Coal Measures, must have 

 accumulated under very different conditions conditions 

 for which it is not easy to find a parallel ; but in any 

 case these deposits afford evidence of very rapid 

 accumulation. 



These considerations will not tempt us, however, to 

 modify our estimate of one foot in a century ; for though 

 in some cases this rate may have been exceeded, in others 

 it may not have been nearly attained. 



Closely connected with the rate of deposition is that of 

 that changing level of land and sea ; in some cases, as in 

 the Wealden delta, subsidence and deposition appear to 

 have proceeded with equal steps, so that we might regard 

 them as transposable terms. It would, therefore, prove of 

 great assistance if we could determine the average rate 

 at which movements of the ground are proceeding ; it 

 might naturally be expected that the accurate records 

 kept by tidal gauges in various parts of the world would 

 afford us some information on this subject ; and no doubt 

 they would, were it not for the singular misbehaviour of 

 the sea, which does not maintain a constant level, its 

 fluctations being due, according to Professor Darwin, to 

 the irregular melting of ice in the polar regions, Of 

 more immediate application are the results of various 

 observations in Scandinavia, which appear to prove an 

 average rise of the peninsula at the rate of 8 feet in 

 a century to be still in progress ; * and Mr. G. K. 

 Gilbert's measurements in the great Lake district of 

 North America, which indicate a tilting of the continent 

 at the rate of 3 inches per hundred miles per century. 



-' See on this question, Suess, " Das Antliz der Erde," vol. ii., and 

 " Grundziige der Physischen Erdkunde," by A. Supan, Leipzig, 1903 

 pp. 341-365. The latter contains a long list of references. 



