66 THE BUILDING OF AN ISLAND. 



to carry lower down the slope and ultimately to the sea. We see that if such 

 a process is continued for ages it must reduce the general level of the island. 

 We also see that the process must be very slow, but must be especiallv so where 

 the rock is very hard and offers great resistance to the preparatory decompos- 

 ing action of the atmosphere. The points and lines, or the areas, where such 

 hard rocks exist, must come gradually to stand higher than the softer material 

 which surrounds them, and thus it is not difificult to understand that the forms 

 of the valleys, and consequently of the hills, is a good deal dependent on the 

 nature of the rocks. 



Of this general truth we may occasionally find striking illustrations. For 

 example, when we drive past the residence of Diamond and Ruby we notice, 

 as we ascend the rising ground from the direction of Christiansted, that there 

 are many hard blocks of limestone lying by the roadside. We do not see, 

 in the cultivated fields, where these blocks have come from; but if we take the 

 road over Carrawall Hill and cross the same rising ground a short distance to 

 the south, we see that a rather thick layer of hard limestone is cut through for 

 the road where it nears the top of the rise. Here we see what it is that has 

 given origin to the large limestone blocks just mentioned, and what it is that 

 has protected this rising ground from the destructive action of the waters com- 

 ing from eastwards; and we see that the whole rise which, as a matter of fact, 

 ci'osses the slope of the strata and the consequent general direction of the drain- 

 age, owes its origin to the existence of this hard bed. In the same connection 

 it may be noted that the tops of the hills often show such hard rocks that we 

 can hardly conceive of their ever being worn away, yet the roughness of their 

 gray lichen-covered sides and their rounded angles give us a hint that, though 

 they may hold out for many centuries, they, too, must finally give way to the 

 destructive forces. Sometimes on the hillsides we meet with large isolated 

 blocks of stone of extreme hardness, whose form shows us that they have been 

 detached from layers of rock higher up the slope, and we wonder how they 

 can ever be worn away; but we, perhaps, find some of them still lower down 

 the hill, and we perceive that they must have been removed from above. But 

 how? Some day, after a storm perhaps, we get a lesson on this point; a large 

 block that we remember to have noticed on the upper side of a road, for ex- 

 ample, has slidden down and now partially blocks the road. This compels our 

 attention, and we reflect that these isolated blocks must in all cases be movina: 

 down the hillside in this wav. Every heavy rain removes something of the 

 soil and the gravel on which the block is resting, and by and by it slides farther 

 down, till finally it will reach the nearest watercourse. In such a watercourse 

 among the hills we may often find some of these large blocks from the slopes; 

 and what happens to them there? Why, that every flood in the watercourse 

 rolls along, bearing sand and pebbles in great quantities past them and over 

 them and grinding them down as the rush goes on, till finally they are worn 

 away and their particles are all carried off to the sea; it mav take centuries, 

 but it will be done. 



