THE BUILDING OF AN ISLAND. 29 



Stones and marls cut througli for the roadway. These beds dip at a moderate 

 anarle to about south-southeast. Thcv, like the beds below them, are full of 

 corals, but they appear to have been put down much later than the rocks in 

 the larg^c quarry. It seems indeed that the two sets are well marked off from 

 each other at West End, that the southerly dipping rocks have been put down 

 over the westerly dipping rocks, and have been tilted at a later time by a 

 movement from the north, the last, perhaps, of the movements that have given 

 the island approximately its present outlines. It is probable, moreover, that 

 the southern dip. mentioned as belonging to the upper rocks at West End, 

 docs not extend very far, but soon gives way southwanls to a horizontal arrange- 

 ment, which is what appears to prevail over the whole of the southwest plain. 



It must be admitted, however, that the geological evidence for the sup- 

 posed anticlinal axis through the northwest hills and continued to seawards 

 through Sandv Point is not strong. It has already been mentioned that the 

 stratification in the big quarry on the east boundary of the town is irregular, 

 and when we examine the different small exposures south of the town and the 

 more important one in the large quarry near the north end of the Salt Pond, 

 the quarry at present being used for procuring limestone for the Central 

 Factory, we see no evidences of a westerly dip, or, indeed, of a dip of any kind. 

 The mass of limestone is not stratified, but suggests deposition in the neigh- 

 bourhood of a reef through a long period of time. Some coral and numerous 

 shell casts are to be seen. The greater part of the rock has been redeposited 

 from solution, is nearly pure calcitc and very hard, often with channels and 

 openings in different parts of the quarry, in which there are clear evidences of 

 the action of underground water. The same is to a great extent true of the 

 o-reat West End quarry, but not of the rocks at the entrance to the town, which 

 are very little altered, are clearly stratified, and contain well-preserved corals, 

 small fragments of molluscous shells and sea-egg spines. The limestone rocks 

 of the west end of the island present, indeed, a difficult, and therefore attrac- 

 tive, subject of study. 



Irregularities. 



The reader who fallows up by actual observations the study of the arrange- 

 ment of the limestone rocks described in the preceding pages, will find 

 occasional irregularities that have not been hitherto mentioned. The princi- 

 pal of these known to the present writer is in the neighbourhood of Sion Hill 

 and on the road from that estate to Sion Farm. Here in the road-cuttings 

 it is sometimes seen that the marl-beds are about horizontal and occasionally 

 dip slightlv to the southeast. This peculiarity appears, however, to be merely 

 local ; for it does not seem possible to trace it through the formation either 

 towards the north or towards the south, all the dips observed in those parts 

 being to southwest or thereabouts. 



Another irregularity, which in this island appears to be of little conse- 

 quence as affecting the arrangement of the rocks on a large scale, is neverthe- 



