1 2 St. J ago. 



PART I. 



be perfectly horizontal ; but for a space of a quarter of 

 a mile directly under the hill, it dips into the sea and 

 disappears. On the south side the dip is gradual, on 

 the north side it is more abrupt, as is shown in the 

 woodcut. As neither the calcareous stratum, nor the 



No. 2. 



SIGNAL POST HILL. 



A— Ancient volcanic rocks. B— Calcareous stratum. 



C— Upper basaltic lava. 



superincumbent basaltic lava (as far as the latter can 

 be distinguished from the more modern ejections), 

 appear to thicken as they dip, I infer that these strata 

 were not originally accumulated in a trough, the 

 centre of which afterwards became a point of eruption ; 

 but that they have subsequently been disturbed and 

 bent. We may suppose either that Signal Post Hill 

 subsided after its elevation with the surrounding country, 

 or that it never was uplifted to the same height with it. 

 This latter seems to me the most probable alternative, 

 for during the slow and equable elevation of this portion 

 of the island, the subterranean motive power, from ex- 

 pending part of its force in repeatedly erupting volcanic 

 matter from beneath this point, would, it is likely, have 

 less force to uplift it. Something of the same kind 

 seems to have occurred near Red Hill, for when tracing 

 upwards the naked streams of lava from near Porto 

 Praya towards the interior of the island, I was strongly 

 induced to suspect, that since the lava had flowed, the 

 slope of the land had been slightly modified, either by a 

 small subsidence near Red Hill, or by that portion of 

 the plain having been uplifted to a less height during 

 the elevation of the whole area. 



