chap. i. Calcareozcs Horizontal Deposit. 1 1 



the same inclination as when deposited round the 

 ancient shores of the island. I found only one inland 

 section, namely, at the base of the hill marked A, where, 

 at the height of some hundred feet, this bed was ex- 

 posed ; it here rested on the usual compact augitic rock 

 associated with wacke, and was covered by the wide- 

 spread sheet of modern basaltic lava. Some exceptions 

 occur to the horizontality of the white stratum : at 

 Quail Island, its upper surface is only forty feet above 

 the level of the sea ; here also the capping of lava is 

 only between twelve and fifteen feet in thickness ; on 

 the other hand, at the NE. side of Porto Pray a 

 harbour, the calcareous stratum, as well as the rock on 

 which it rests, attain a height above the average level : 

 the inequality of level in these two cases is not, as I 

 believe, owing to unequal elevation, but to original 

 irregularities at the bottom of the sea. Of this fact, at 

 Quail Island, there was clear evidence in the calcareous 

 deposit being in one part of much greater than the 

 average thickness, and in another part being entirely 

 absent; in this latter case, the modern basaltic lavas 

 rested directly on those of more ancient origin. 



Under Signal Post Hill, the white stratum dips 

 into the sea in a remarkable manner. This hill is 

 conical, 450 feet in height, and retains some traces of 

 having had a crateriform structure ; it is composed 

 chiefly of matter erupted posteriorly to the elevation of 

 the great basaltic plain, but partly of lava of apparently 

 submarine origin and of considerable antiquity. The 

 surrounding plain, as well as the eastern flank of this 

 hill/ have been worn into steep precipices, overhanging 

 the sea. In these precipices, the white calcareous 

 stratum may be seen, at the height of about 70 feet 

 above the beach, running for some miles both north- 

 ward and southward of the hill, in a line appearing to 

 2 



