Uniformity in Geological Change 



within the historical period has not amounted 

 to many yards, but the greater extent of ante- 

 cedent upheaval is proved by the occurrence 

 in inland spots, several hundred feet high, of 

 deposits filled with fossil shells of species now 

 living either in the ocean or the Baltic. 



It must in general be more difficult to detect 

 proofs of slow and gradual subsidence than of 

 elevation, but the theory which accounts for the 

 form of circular coral reefs and lagoon islands, 

 and which will be explained in the concluding 

 chapter of this work, will satisfy the reader that 

 there are spaces on the globe, several thousand 

 miles in circumference, throughout which the 

 downward movement has predominated for ages, 

 and yet the land has never, in a single instance, 

 gone down suddenly for several hundred feet at 

 once. Yet geology demonstrates that the per- 

 sistency of subterranean movements in one direc- 

 tion has not been perpetual throughout all past 

 time. There have been great oscillations of 

 level, by which a surface of dry land has been 

 submerged to a depth of several thousand feet, 

 and then at a period long subsequent raised 

 again and made to emerge. Nor have the regions 

 now motionless been always at rest; and some 

 of those which are at present the theatres of re- 

 iterated earthquakes have formerly enjoyed a 

 long continuance of tranquillity. But, although 

 disturbances have ceased after having long pre- 

 vailed, or have recommenced after a suspension 

 for ages, there has been no universal disruption 

 119 



