346 Maw — On Watersheds. 



the present contour of the land, any zone of equal height on the 

 land ought approximately to represent an ancient sea margin, and on 

 the re-submergence of the land the coast ought to take up nearly its 

 old position ; but lines of equal height on the land surface and neigh- 

 bouruig coast line have little or no relation to each other, and are 

 generally not only different in their direction but also in the char- 

 acter of their outline ; and the same difference of character will be 

 observable between a coast line produced by submergence without 

 erosion, and one moulded by denudation. The prevailing tendency 

 of the denuding sea-line is to be straight, and of a simply submerged 

 coast, or of lines of equal height on the land, to be sinuous, bending 

 round the ramifying valleys of the watershed system quite unhke 

 the most sinuous coast cliff. 



This is not so obvious to the eye in an actual view, because the 

 sight cannot grasp at a glance a sufficient area, but if you follow it 

 from the coast inland, and return to the sea at the same height at its 

 other end, you will find that you have travelled in a very different 

 direction, and a manifold greater distance than the line taken by the 

 sea ; and when the land line is plotted down on paper it will exhibit 

 a kind of structmre very unlike that of the adjacent sea-board. In 

 fact, the sea, in its erosive action on the coast, takes little or no account 

 of the surface contour of the land ; it denudes back the high land in 

 the shape of cliffs pretty nearly at the same rate as the lower ground 

 of intersecting chines and combes, cutting indiscriminately across, 

 and obliterating both hills and valleys, and working on a sort of 

 jagged straight line singularly different to the winding line repre- 

 senting the lines of equal height on the land, which ought, according 

 to the marine theory, to represent ancient coast lines of sea erosion. : 



Will the advocates of marine denudation, who assume that the sea 

 excavated the glens and chines, intersecting the present sea cliffs 

 (and many of them if prolonged would extend far below the present 

 sea margin), explain why it is that the sea utterly ignores the old 

 outline assumed for it, and follows one entirely different ? Instead of 

 running up the valleys that are assumed to have been the result of 

 its former action, and leaving the separating promontories untouched, 

 as it must have originally done on the marine theory, how is it that 

 it now breaks across both indiscriminately and removes with the same 

 apparent ease a cliff 200 feet high and the low land that gently 

 slopes down the glens under the sea ? The coast of the Isle of Wight, 

 and the cliffs to the east of Hastings, well illustrate the form of 

 outliue on which coast erosion really works. 



The subjoined engraving^ of part of the coast at Port Eoyal, 

 Jamaica, represents one of the very few authenticated cases of recent 

 submergence, and affords a good example of the striking difference 

 between a coast line produced by submergence following the form of 

 the surface, and the ordinary coast line produced by marine erosion. 



The coast at Port Eoyal, Jamaica, is known to have undergone a 

 sudden subsidence in the year 1692, and has assumed an intricate 

 outline notably distinct from any cliff-girt shore, and just the sort of 

 1 Copied from the map appended to the Keport of the Jamaica Commission. 



