14 THE BUILDING- OK AN ISLAND. 



all of which arc covered with a fleshy coat in which the small stars are em- 

 bedded, a coat which contains some lime, and this frequently in delinite forms 

 that may be often seen as grains forming part of the sand of the seashore. 



Another stonv form that exists on the reefs, and on some of them in 

 great abundance, is the viillcpore coral, of which the naturalists tell us that the 

 living creature that covers it and occupies the thousands of tinv holes which 

 give it its name, does not belong to any of the great groups above mentioned, 

 but forms a class bv itself. Like the true corals and their allies, it contributes, 

 however, to the material forming the sea bottom around our shores. 



The corals of all kinds contribute, however, only a comparatively small 

 portion of the materials accumulating on the surface of the submarine Santa 

 Cruz. An examination of the bottom with the aid of a sea-glass will help us 

 to understand how the sand which covers that great area has been formed, and 

 how it is continually increasing. The glass in question is simply a watertight 

 box open at one end and covered with a sheet of glass at the other; the glass 

 being pressed down on the surface of the water gets rid of all the small ripples 

 which ordinarilv prevent our seeing what is at the bottom, and then every- 

 thing, corals, seaweeds, sea-eggs, starfish, or whatever it may be. becomes 

 quite distinct. We mav also learn much by taking up samples of the sand 

 from the bottom and from the seashore, and examining them with the help 

 of our lens. 



We shall find that the sand is supplied by many living agencies, which in 

 turn obtain the material from the clear sea-water. Among many other sub- 

 stances dissolved in it, the sea-water contains carbonate of lime. Many sea- 

 weeds have the power of extracting this carbonate of lime, and some of tiiem 

 in such a remarkable degree that thev come at last to be almost entirel\ com- 

 posed of it. When they die and break up they form a large proportion of the 

 sand in some places, for instance at the Round Reef in Christiansted harbour, 

 where one well-known seaweed is verv conspicuous as a component of the sand. 

 Other lime-loving weeds have some general resemblance to corals and are 

 known as " corallines"; others again, which mostly encrust rocks, resemble en- 

 crusting corals, but from possessing no openings have been called " nuUipores." 



Sea animals, feeding on the weeds, find the lime for various parts of their 

 bodies, as the shells of molluscs, from the gigantic conch down to the tiny 

 limpet clinging to the rock on the shore, or the shells and spines of sea-eggs, 

 or sea-stars, foraminiferous shells, the shells of crustaceans, and so on. All 

 these creatures, at their death, whether violent or natural, leave the solid parts 

 of their bodies as a Icgacv to the sheet of material forming on the sea bottom. 

 When such remains are near the shore thev are driven upon it and are broken 

 by the action of the waves into coarse or fine fragments, or are even ground 



The following notes of the contents of a sample of sand taken by the writer from the beach at Cane 

 Bay on the north shore of the island will serve to show how varied are the sources of our sea-sand. The 

 sample was gathered at the wave-margin, and is not so worn as the ordinary beach-sand at the same spot. 



The following was the compo.sition of three small portions examined, the grains being separated i^artly 

 with and partly without the aid of a lens : (See ne.xt page). 



