THE GEOLOGIST. 



33 



M. Gaudin has likewise been very successful of late in the pro- 

 duction of artificial minerals. He has given us a recipe for making 

 sapphires in a few minutes, with hardly any ti'ouble and at an 

 extremely small expense. We know that the precious stones 

 Corindon, Buby, Sapphire, &c., are essentially formed of pure 

 alumina, colored by very minute quantities of certain substances, 

 the nature of which has not yet been perfectly determined. j\L 

 Gaudin, some time ago, obtained artificial rubies by melting 

 alumina with a ver}' small quantity of chromate of potash, but the 

 process was rather a dif&cult one. He has lately made known an 

 easier method by which he obtained an infinite number of minute 

 cr\'stals of alumina ; these ciystals were found to be, for the most 

 part, transparent hexagonal tables, amongst which were seen 

 smaller ones, quite red, and of a rhomboidal form. ]Most of them 

 were exceedingly minute, and theii' forms could only be thoroughly 

 examined by the aid of a microscope, but, since then ciystals 

 large enough to serve as pivots in watches, &c., have been ob- 

 tained. The experiment just refeiTed to furnishes us vdth. another 

 incontestable proof that the hard mineral substances presented to 

 us in nature under erystalized forms, have been produced by the 

 agency of heat, and have certainly not been deposited from water, 

 as the crystals produced in oui' laboratories, fi^om solutions, or like 

 the beautiful calcareous spar which is forming every day under our 

 eyes, in the grottos of limestone districts. 



M. Tessier on presenting to the Paris Academy of Sciences, last 

 October, a piece of j)etiified wood from a submerged forest on the 

 west of Normandy, spoke of an interesting geological phenomenon 

 which is taking place daily on the French coasts. It appears from 

 his statements, that whilst the ^MediteiTaneanSea is slowly retiring 

 from the south coast of France, rendeiing these shores yearly 

 broader and broader by the new made land or muddy deposits it 

 is leaving behind, the North Sea, on the conti^aiy, is forcing its 

 way slowly but surely on the north-western coasts, gradually en- 

 croaching more and more upon the continent, and penetrating, in 

 some places, to a considerable distance, into the neighbouring dry 

 land. That this phenomenon has been at work for some time is 

 proved by the fact that the ancient lighthouse of Boulogne, 

 elevated duiing the reign of Caligula, and which ^ as still standing in 

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