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Show NoTE XXIV. GRANITE. the fiffures of granite or porphyry quartz is formed ; in the fiffi1res of limefl:onc calcareous fpar is produced. g. During thefe firfi great volcanic fires it is probable the atmofphere was either produced, or much incre::~fed; a procefs which is perl1aps now going on in the moon ; Mr. Herfchell haviug difcovcred a volcanic 'cr::~ter three miles broad buming on her difk. 10. The fummits of the new mountains were cracked into innumerable lozenges by the cold dews or fnows falling upon them when red hot. From thefe fummits, which were then twice as high as at prefent, cubes and lozenges of granite, and bafalt, and guartz in fome countries, and of marble and flints in others, defcended gradually into the valleys, and were rolled together in the beds of rivers, (which were then fo large as to occupy the whole valleys, which they now only interfeCl ;) and produced the grc:Jt bed ~ of gravel, of which many vnlleys confifl:. 11. In ferer:~l parts of the earth's furface fubfequent earthquakes, from the fermentation of moraffes, have at ~rent periods of time deranged the pofition of the matters above dcfcribed. Hence the gravel , which was before in the beds of rivers, has in fame places been raifed into mountains, along with clay and coal fl:rata which were formed from moraffes and wafhed down from eminences into the beds of rivers or the neighbouring feas, and in part raifed again with gravel or marine !hells over them ; but this has on! y obtained in few places compared with the general dill:ribution of fuch materials. Hence there feem to have exifl:ed two fources of earthquakes, which have occurred at great difl:ance of time from each other; one from the granite beds in the central parts of the earth, and the other from the moraffes on its furface. All the fubfequent earthquakes and volcanos of modern days compared with thefe are of fmall extent and infignificant effeB:. 12. Befides the argillaceous fand-fione produced from moraffes, which is firatified with clay, and coal, and iron, other great beds of filiceous fand have been formed in the fea by the combination of an unknown acid from moraffes, and the calcareous matters of the ocean. 13. The warm waters which are found in many courrtries, are 0wing to fl:eam arifing from great depths through the fiffures of limell:one or lava, elevated by fubtcrranean fires, and condenfed between the firata of the hills over them; and not from any decompoGtion of pyrites or manganefe near the furface of the earth. q .. The columns of bafaltes have been raifed by the congelation or cxp:mfion of granite beds in the aa of cooling from their femi-vitreous fufion. I 2 |
