1870.] Notes on the Geology of the Vicinity of Port Blair. 233 



merely landslips of the superficial humus which must occur to a 

 great extent wherever on steep or elevated ground primeval jungle 

 has been cut down and the surface exposed to direct atmospheric 

 influences, but to landslips of the rock itself. 



Water passing through the permeable sandstones, and being ar- 

 rested on the surface of the impermeable shales, produces a slide 

 down which the superincumbent mass, resting at an inclination 

 of from 55° to 60°, must tend to slip, the rapidity with which such 

 destruction takes place being in a direct ratio to that of the re- 

 moval of the lower portions of the beds by the sea or other agen- 

 cies. Such being the condition of the rocks on Eoss Island, it was 

 with surprise that I saw that it had been the practice and was still 

 so at the time of my visit, not only to remove and use for building 

 purposes the stones on the beach which serve to break the force of 

 the waves, but even to quarry out large masses from the face of the 

 beds, thus endangering the stability of the island. 



On the eastern or seaward side, the destruction is progressing 

 in a different way. The escarpment shews a steady tendency in 

 the edges of the beds to break up ; and confused heaps of fallen rock 

 and clay abound. Sections of the road too, constantly slide down 

 and so bring more and more of the rocks and their natural covering 

 within the range of the wash of the waves. 



The highest point of Eoss is 195 feet and the area about one-third 

 of a square mile. As the principal buildings of the settlement are 

 upon this small island, it should be an object of no trifling importance 

 to preserve its integrity to the utmost. With this in view, it is per- 

 fectly obvious that the practice of removing stones from the beach 

 and of quarrying them out of the side of the island should be discon- 

 tinued. Some protective measures to retain the soil and shelter the 

 rocks from the direct action of the atmosphere might be undertaken 

 with advantage. 



Under this head the planting of trees especially of those species 

 known to have roots which bind the soil (thus to a certain extent 

 reviving the conditions which existed before the jungle was cut 

 down,) would be perhaps the most efficacious. 



Southern Coast line or Port Blair. — An examination of the 

 rocks exposed along the coast line from Aberdeen round by Haddo 



