I70 SEA AND LAND 



two hundred feet or more. Somewhat later this region was 

 elevated to a height a Httle above its present level. This 

 resurgence from the deep was followed by yet another down- 

 sinking, probably of relatively slight amount, but suf^cient to 

 carrv many areas of forested lands below the level of the tide. 



In the region about the Dismal Swamp of Virginia, the 

 present writer has ascertained that there have been at least 

 three periods of successive elevation and subsidence, during 

 which the land swayed up and down through a range of about 

 fifty feet of altitude within a period which is probably to be 

 reckoned as of no greater duration than the time that has 

 elapsed since the last great invasion of ice began in the north- 

 ern part of the continent. Athough the study which has been 

 applied to the subject of land swayings is still very incomplete, 

 the results are sufficient to assure us that such instances as 

 have been given are by no means exceptional. They have 

 been indeed common in all stages of the earth's history which 

 are legibly chronicled in the pages of the great stone book 

 whose leaves are the strata of the earth's crust. It is proba- 

 ble, however, that these movements of the land are often 

 greatest next the shores ; they may indeed occur there with- 

 out corresponding alterations in the level of the interior parts 

 of the continent. 



As yet geologists have not satisfactorily traced the several 

 causes which cooperate to bring about these upward and 

 downward movements of the earth's crust. They have, how- 

 ever, become convinced tliat the old idea to the effect that the 

 land masses were in some way permanently and rigidly upheld, 

 like the arclies of solid masonry, is an error. They are driven 

 to conceive these parts of the crust which are above the level 

 of the sea, as well as much of the ocean floor near the con- 



