GULLIVER. — SHORELINE TOPOGRAPHY. 189 



Superposed Drainage. — No attempt has been made in this study to 

 work out the sequential stages in the fading of elevated shorelines. This 

 problem is intimately connected with the dissection of the land, and de- 

 pends largely upon the factors which control such dissection in any given 

 locality. The shore deposits being coarser would probably remain longer 

 than those finer materials laid further out from the old shore. When 

 however all the shore deposits themselves are eroded away, the amount 

 of the former coastal plain overlap may frequently be inferred from the 

 arrangement of the streams. Where there never had been a cover, the 

 adjustment of the drainage to the structure would be more perfect than 

 where the streams had taken consequent courses over an uplifted coastal 

 plain. The coastal plain sediments would overlie uncomformably what- 

 ever structures happened to occur in the oflTshorc region of the previous 

 cycle, and thus the streams in cutting through the cover would have 

 many chances to become superposed upon unexpected dithculties be- 

 neath.* The line between the region of well adjusted drainage and the 

 region in which superposition of streams is found represents a former 

 shoreline, now elevated and in a late sequential stage. 



9. Islands. 



Consumption hy the Sea. — As a part of the sea's work to reduce all the 

 land to a submarine platform just above wave-base, the islands formed by 

 the depression of a region are some of thirst forms to be demolished. 

 Very small islets are quickly reduced to skerries and to submarine reefs. 

 Large islands are more continental in character, and their coasts may 

 become mature long before the islands themselves are consumed. These 

 larger islands are not as a rule tied to the mainland by bars. But 

 islands, which range in size from an area of one third of a square mile 

 up to some two hundred square miles, are very frequently tied to the 

 mainland by bars in the process of their demolition by the sea. 



Upon the coast of Italy where island-tying in its various stages is beau- 

 tifully shown, such a bar is called a tombolo.f For convenience in 

 distinguishing island-tying bars from those of other kinds, the writer 

 proposes to call every bar of this kind a tombolo, giving an English 

 plural tombolos. 



Loop-bar: Shnpka, Figure 12. — An island at some distance from the 

 mainland may be so large that the sea cannot dispose of all the detritus 



* See fuller statement by Professor Davis, Lond. Geog. Jour., 1895, V. 128-138. 

 t See Figure 16. 



