THE GEOLOGIST. 
83 
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 trouble and at an 
extremely small expense. We know that the precious stones 
Corindon, Ruby, Sapphire, &c., ai'e essentially formed of pure 
alumina, colored by very minute quantities of certain substances, 
the nature of which has not yet been perfectly determined. M. 
Gaudin, some time ago, obtamed artificial rubies by melting 
alumina with a very small quantity of chromate of potash, but the 
process was rather a difficult one. He has lately made known an 
easier method by which he obtained an infinite number of minute 
crystals of alumina ; these crystals 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 exceedmgly minute, and their forms could only be thoroughly 
examined by the aid of a microscope, but, since then crystals 
large enough to serve as pivots in watches, &c., have been ob- 
tained. The experiment just referred to furnishes us with another 
incontestable proof that the hard mineral substances presented to 
us in nature under ciystalized forms, have been produced by the 
agency of heat, and have certainly not been deposited from water, 
as the crystals produced in oiu- laboratories, from solutions, or Uke 
the beautiful calcareous spar which is forming every day luider our 
eyes, in the grottos of limestone districts. 
M. Tessier on presenting to the Paris Academy of Sciences, last 
October, a piece of petrified 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 Mediten-aneanSea is slowly retiring 
from the south coast of France, rendering these shores yearly 
broader and broader by the new made land or muddy deposits it 
is leaving behind, the North Sea, on the contrary, 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 during the reign of Caligula, and which Mas stiU standing in 
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