the building of an island. 7 



The Rocks ok the Island. 



The above sketch of the geograph\' of the island may perhaps be sufficient 

 as an introduction to our study of its structure; further details may be noticed 

 as we proceed. 



The surface described is clothed nearly everywhere with vegetation, which 

 to a great extent hides the soil. In the cultivated parts of the island, how ever, 

 we may often see large areas of the soil exposed, antl in the uncultivated 

 portions the sides of the watercourses and the cuts made by the small rills 

 running down the hillsides also afford us peeps at the soil and the subsoil. 

 When now we take advantage of these various opportunities, and examine the 

 soils in different parts of the island we soon see that they differ very considerably 

 from eacii other, and if we examine the stones found in them we find that they 

 also vary a good deal. Sometimes, moreover, we get to see, in road-cuttings 

 and elsewhere, what lies beloiv the soil, that is to say we get to see some of the 

 substances which make up the solid mass of our island, and we soon perceive 

 that thev too show noticeable differences. In some cases they differ only slightly 

 from each other and we mav put them in the same class; but in other cases 

 thev differ so much that we have to put them in separate classes. If we take 

 our specimens from any quarry or " gravel pit " in the East End or from the 

 hills of the north and west we shall find that they generalh' bear a great re- 

 semblance to each other; they most frequently have a rusty look, especially 

 those that have been long exposed to the weather. These sometimes crumble 

 to pieces and are then often spoken of as "rotten rock"; but if we go deeper 

 into the rock in the quarry and break a piece through, we find that it is hard 

 and crystalline and most often has a bluish or grey colour. These colours are 

 also often shown very plainly on the roads where the rock has been worn bv 

 the traffic, and in a still more striking wav in the pieces that have been broken 

 out of the cliffs by the force of the waves and have afterwards been rolled about 

 and rounded on the sea beach. Hence the common local name for the hard 

 rock from which these pebbles and boulders have been formed is" blue-beach." 

 With some interesting and important exceptions to be noted later, this is the 

 rock which we shall find from Christiansted eastwards, throughout the easicrtt 

 trianoic and also throuafh the northwest district of the island ; but if we take 

 our specimens from the neck which intervenes between those two parts, or, to 

 speak more accurately, from the Central Slope, we shall find something very 

 different. Here the rocks are mostly white or creamy in colour. Sometimes 

 thev are soft and are known as marls, sometimes they are hard and are called 

 limestones, or locally, "marl-stones." In either case it is easy to see that they 

 must be placed in a quite separate class from the blue-beach rocks. 



Before proceeding further, however, it should be noted that the word 

 "rock ". is used by geologists in a peculiar sense. While in daily language a 

 "rock " means a mass of liard stone, in geological language it means any mass 

 of material that goes to make up the crust of our earth ; hence beds of sand 



