THE LESSONS OF GALVESTON 381 



spoiiding to the islands south of Mississippi Sound and forming a 

 direct submarine connection (save as cut off by the delta) between 

 these islands of the eastern Gulf and the well developed ke3'S of the 

 southern 'J'exas shore. The position of these banks, like that of the 

 Horn Island and its fellows, is such as to demonstrate that the waters 

 have invaded the mainland, and that west of the delta the encroach- 

 ment has been sufficient not merely to push back the shoreline 50 

 to 100 miles but to completel}'' submerge the ancient keys. The most 

 striking feature of these drowned and half-drowned keys is their 

 symmetric arrangement; except for the interruption b}^ the delta 

 (with its new and lesser sand banks), the great bars form a sweeping 

 curve regular as the beach line of a land-locked bay, and hence afford 

 a rough measure of the outbuilding of the delta as well as of the in- 

 vasion of the Gulf on its flanks. Hardly less striking than the sym- 

 metry of the series is the closeness of continuity between keys and 

 banks ; and it is a significant fact that Galveston Island is the north- 

 eastern terminus of the west-coast system of keys, the last stretch of 

 these sand banks still rising above the level of tide. 



It is the business of the geologist to detect and weigh the evi- 

 dences of subsidence or elevation of coasts and to estimate the rates 

 of movement for the guidance of local residents and investors; and 

 it behooves such citizens to avail themselves of the scientific re- 

 searches. The observations on the rise and fall of various coasts are 

 impressive: Holland derives its name from its subsidence, coupled 

 with the building of dikes for the protection of the land; the Island 

 of Batavia, inhabited in the days of Tacitus, is drowned ; Zuyder 

 Zee was formed by an invasion of the sea about the end of the 13th 

 century, and the Netherland ])olders (or dike-protected lands) are 

 maintained only b}' artificial embankments which have been raised 

 from generation to generation until now cultivated fieUls lie 7 to 

 10 meters Ijelow tide level. The measure of the rate of subsidence 

 of the Holland coast ranges from .09 to .75 m.eter per century ; since 

 1732 the mean has been .26 meter, or nearly a foot, per century. 

 The subsidence of the New Jersey coast was estimated at two feet 

 per centur}' by State Geologist Cook ; it has continued so long that 

 fresh-water cedar swam |)S have been submerged and the forests im- 

 bedded in saline mucks, whence it is a profital^le business to mine the 

 logs for lumber; and in consequence of the current sinking the At- 

 lantic is encroaching and swallowing or destroying estates and homes 

 to the value of man}' thousand dollars annually. The subsidence 



