70 SPOLIA ZEYLANICA. 



A characteristic feature of the plateau is that there is a slight 

 deepening — a sort of irregular channel — running along its central 

 line and parallel to the outer edge throughout nearly the whole of 

 its length. 



Where the plateau is of an average depth of 35 fathoms this 

 depression is, roughly speaking, of a depth of 42 fathoms ; and 

 where, as off Moratuwa, the general depth is 23 fathoms, the 

 depression is about 33 fathoms. Near Colombo, however, this feature 

 becomes lost ; and, instead of a depression, there is, on the other 

 hand, a series of banks : one with a depth of but 10 fathoms, the 

 others less shallow. 



The 20-fathom line also, which gradually increases its distance 

 from the coast between Galle and Mount Lavinia, takes a most 

 decided bend outward at this point, ^nd, together with the banks 

 referred to, causes a marked general shoaling on the plateau in this 

 neighbourhood. 



Fig. II. represents a section taken from the " Haycock " (Hini- 

 dumakanda) to the coast at a spot about ten miles eastward of 

 GaUe and through the narrowest part of the plateau. 



Fig, III. gives a section from the same mountain through Waal 

 island (at the south-west corner of Ceylon), and again through the 

 plateau into the deep water beyond, the plateau at this point being 

 of average width and normal character. The vertical scale in each 

 case is the same as the horizontal scale, so that the plateau and the 

 faU into deep water are shown with their true relativity, though the 

 central gully is scarcely realized. 



A section taken through Colombo would exhibit very similar 

 features to both figs. I. and II. as regards the plateau, but the land 

 being low and level for many miles inland it would scarcely be 

 apparent as an elevation on this scale, which is 6,000 feet to one 

 inch. 



The above Qharacteristics may therefore be thus summarized : — 



(1) The plateau extends on an average to a distance of twelve 

 miles from the coast with depths slowly shoaling from the south- 

 ward to the northward from 40 to 20 fathoms. 



(2) In all parts a sudden and very weU-marked drop into oceanic 

 depths occurs at the outer edge. 



(3) A slightly depper channel or guUy is found in the centre, 

 tapering off to the northward, and ended by 



(4) A marked shoaling, and the existence of banks, beginning off 

 Mount Lavinia and extending to the northward. 



n. — Effect of the Plateau upon Current and Swell. 



It must be supposed that such a natural barrier fringing the coast 

 would cause some considerable modification in the direction and 

 cjpeed of the ocean currents reaching the vicinit}^ of Ceylon, as 



