ON THE UKOLOGY OF nAHHAUOM. 219 



from -0 to 30 feet high. It is evident tliiii tliis lidgo is ])art of 

 the original nucleus of the island when it first rose above the sea, 

 and that the plateau of coral-rock which terminates in the low 

 escari)ment is part of the earliest encircling coral-reef. Its original 

 houndary-line doubtless lay along the western sloi)e of the ridge, 

 and has been cut back to its present position and scarped by the 

 action of rain and running water. From Chimborazo the ridge 

 curves westward, and though somewhat broken near Caledonia it 

 can be traced to Mount Hillaby, where it rises to over 1100 feet: 

 thence it runs north-westward to .Spring estate, where it passes 

 beneath the coral-rock almost at right angles to the course of the 

 latter, in the same way as it started at Castle Grant. 



The boundary of the coral-rock conforms roughly to the zigzag 

 course of this ridge, lying always on its southern and western sides, 

 and always presenting an escarpment of greater or less height. 

 Its edge has been cut back irregularly, and it is trenched in some 

 places by deep gullies which are continuations of the w^atercourses 

 that traverse the western slopes of the Hillaby ridge. Near Hillaby 

 Plantation the layers of coral-rock have a distinct westerly dip or 

 slope away from the Hillaby ridge ; the direction varies from a 

 little S. to a little N. of W., and the angle of slope is about 4'. This 

 inclination is probably due in part to original formation on a slope, 

 but it may have been increased by subsequent upheaval. 



From near Hillaby to Spring estate the coral-rock lies directly 

 on the Scotland beds, its boundary-line running first ]^. and then 

 \V., while the dominant ridge outside runs also X. and W.N.W. 

 under the coral at Spring. This place is 923 feet above the sea, 

 and here the escarpment begins to present bolder features again, 

 forming a continuous ridge which overlooks the slopes to the W. 

 instead of being itself dominated by a ridge of older rocks. The 

 escarpment thence runs due north for some distance, and preserves 

 its height as far as Farley Hill and Grenade Hall. Thence it 

 trends to the north-east, and both its base and its summit-level 

 steadily descend just as the levels of the corresponding escarpment 

 descend southward from Hackleston's Cliifs. West of Pico Teneriffe 

 it merges into lower terraces which are probably banked against it, 

 but its continuation may be traced in a line of inland cliffs which 

 set in to the northw^ard and run for about a mile to the north-west, 

 terminating near Cave in the parish of St. Lucy. 



(e) Terraces and Patches of Coral-rod- hclow and luesf of the 

 Escarpment. — From the account of the escarpment which we have 

 given above it is clear that this feature began to be established at a 

 very early period in the history of the island, and, once started on 

 the higher ground, it would tend to extend itself through the subse- 

 quently formed reefs as they were raised above the sea. The original 

 island may have been encircled by reefs, but if so those which 

 covered the nortli-eastern side have been removed by erosion, and 

 as soon as the streams had cut down to the Scotland rocks the 

 muddy water poured into the sea would prevent the growth of 

 corals, except here and there in favourable situations. 



AVhere, however, the escarpment came near the sea along the 



