PRIMARY LIMESTONE AND CORAL ISLANDS. 



75 



Neither in England nor Wales, have any rocks of limestone been 

 found, which possess the crystalline translucent qualities of statuary 

 marble, though very beautiful marbles occur which will receive a 

 high polish ; these belong to the limestone which will be described 

 in the following chapter. White marble is procured from Italy, 

 Switzerland and the Grecian Archipelago. 



Imperfectly white crystalline limestone occurs in different parts of 

 Scotland, intermixed with serpentine and mica slate. Crystalline 

 limestone is found also in the Hebrides, particularly, in the Isle of 

 Sky ; but, it well deserves attention that this limestone, in the latter 

 island, evidently appears to be secondary limestone (lias,) changed 

 in its character, by its contiguity to trap rocks, which were, in all 

 probability, in a state of igneous fusion. In other alpine districts, 

 the limestones called primary, appear, also, to have derived their 

 crystalline character from the action of igneous rocks in their vicinity, 

 and hence, ought not to be classed with primary formations. I have 

 seen in the Alps, many beds of extremely hard white limestone, which 

 have all the characters of primary limestone, with the exception of 

 being somewhat less granular. These beds occur over other beds, 

 containing the fossils found in green sand, and may, therefore, be 

 classed with chalk. That the highly crystalline limestone which oc- 

 curs near primary mountains has been in a state of fusion, is rendered 

 probable by the crystals of garnet and siliceous minerals which are 

 often imbedded in it. These minerals could not have been deposi- 

 ted from an aqueous solution. 



It was once supposed, that all calcareous rocks and strata were 

 composed of the shells of marine animals, and it cannot be doubted, 

 that many of them are entirely formed of these organic remains : 

 but, in the beds of primary limestone, and even in some of the sec- 

 ondary hmestones, no vestiges of such remains occur. It may be 

 said, that the process by which primary limestone was crystallized, 

 destroyed all traces of organization ; and though it would be impos- 

 sible to disprove this, yet there is no reason to belive that lime may 

 not exist as an elementary earth, like siJex or alumine, independent 

 of the operations of animal life. It does so exist, as a component 

 part of many minerals, and it may have existed in sufficient quantity 

 to form the mountains of primary limestone. 



It is, however, a curious but undoubted fact, that no inconsidera- 

 ble portion of the earth's surface has been formed by organic secre- 

 tion ; and the process is still going on, extensively, in the Pacific and 

 Indian seas, where multitudes of coral islands emerge above the 

 waves, and coral shoals and reefs occur, at small depths beneath the 

 water, in which, according to the observations of MM. Quoi and 

 Gaimard, the animals may be seen. " Some spread out into fans, 

 or ramify into trees ; some are round like balls ; their varied and 

 elegant forms mingle and blend together, and reflect the varied hues 

 of red, blue and yellow." As one generation dies and leaves its 



