PLUTONIC OR IGNEOUS ROCKS. 



645 



geologists proposed the substitution of Sinaite for Sienite, but the suggestion has not been 

 adopted. In the Malvern Hills, and those of Charnwood Forest in Leicestershire, com 

 mon granite is found frequently passing into the sienitic variety, in the same bed. 



Diorite or greenstone is but little different from the sienite, containing a larger pro 

 portion of hornblende or augite ; the latter an earthy mineral, usually of a greenish 

 hue. It might therefore be called dioritic granite. The block out of which the head 

 of Memnon (in the British Museum) has been hewn, exhibits an instance of sienite 

 passing into greenstone in the same mass. 



Hypersthenic granite is another variety, formed by scattered crystals of mica in 

 an admixture of quartz and hypersthene, an earthy mineral, so denominated from the 

 Greek, in allusion to its difficult frangibility. 



Granite forms what may be called the skeleton of the solid crust of the earth, of which 

 the various systems of strata are the clothing ; for wherever these are seen to their very 

 base, they are invariably found in all parts of the world to rest on true granite, or some of 

 its varieties. It follows, that any idea formed of its diffusion from what meets the eye 

 is fallacious, for the superincumbent strata, in layers of enormous thickness, shroud 

 it from the observation of man. It may be regarded as a universally diffused rock, 

 entering into the composition of the whole lower portion of the solid shell of the globe. 

 But in various parts of the world it appears at the surface, rising in lofty mountains 

 above it. The chief localities are : 



Great Britain Cornwall, Devon, North "Wales, Malvern Hills, Charnwood Forest, 

 Cumberland, the Highlands of Scotland, Isle of Arran, the Wicklow Mountains in Ireland. 



Europe Finland, the Dofrafield Mountains, the Hartz, the Black Forest, the Alps, 

 the Pyrenees, the Carpathians, and Central France. 



Asia Siberia, the Caucasian, Uralian, Altai, and Himmalayan ranges. 



Africa Mountains of Upper Egypt, the Atlas Mountains, at the Cape of Good Hope, 

 where it forms the base of the Table Mountain. 



America Cape Horn, the Andes, sides of the Orinoco, Venezuela, Mexico, New 

 York, Pennsylvania and Virginia, Greenland, Melville Island. 



In the higher mountains of the Swiss Alps, granite is usually confined to the base, 

 the summits consisting of sedimentary strata ; but in those of Savoy, protogine, a granitic 

 variety, in which there is little or no mica, but talc or chlorite, or steatite in its place, 

 appears at their very crests, forming the top of Mont Blanc, which rises to the height 

 of upwards of fifteen thousand feet above the level of the sea. The Himmalaya range 

 ascends to a far greater altitude, but the uppermost ridges appear to be composed of 

 stratified rocks ; and the summits of Chimborazo, Antisana, and Pichincha, in the Andean 

 chain, consist of vast masses of porphyry, basalt, and modern volcanic matter, the granite 

 only appearing at the height of between eleven and twelve thousand feet. When Hum- 

 boldt was exploring the Andes, he found the granite so covered over with other rocks, 

 that he thought a person might travel for years through the mountain districts of Peru, 

 without even suspecting its existence there. Probably, therefore, in the instance of Mont 

 Blanc, granite occurs at its greatest elevation upon the face of the globe. Saussure reached 

 its crest in the year 1787, after eighteen hours' hard and incessant labour, besides several 

 spent in repose and refreshment. At four o'clock in the afternoon of the second day occu 

 pied in the journey, he pitched his tent on the second of the three great plains of snow in 

 tervening between Chamouni and the top, nine thousand three hundred feet above the level 

 of the sea. The next day the summit was gained at eleven o'clock, where he remained five 

 hours, and made many observations. " From this elevated observatory," he states, " I could 

 take in at one view, without changing my place, the whole of the grand phenomenon of 

 these mountains ; namely, the position and arrangement of the beds of which they are 



