308 Geological Society. 
advanced, to the depth of IZ inch. There was some dust lying in 
the intervals between the crystals, which he blew off; and he ob- 
served that the wind had previously scattered some of it around 
the stone as it lay on the earth. Struck with this singular ap- 
pearance, and almost instantaneously seizing the hint from na- 
fure, Mons, Methuon raised with sticks an appropriate shelter, 
under which he placed the mineral, and frequently paid a visit 
to the apparatus. The elongation of the crystals and the ac- 
eompanying decomposition of the stone, became every Gay more 
visible, until, at the end of two months, the former were nearly 
double in size, and the /utter had increased in proportion. 
_ This discovery of the alum,” exclaims M. Methuon, ‘‘ being 
formed in the air, and not in water, made a strong impression 
apon me, and I confess I could not forbear thinking there existed 
some analogy between this formation, and that of the earthy and 
metallic erystals not of a saline nature. It was evident, indeed, 
that the alum, in this case, did not exist in the rock, but was 
the immediate effect of its decomposition ; that a portion of the 
sulphur from the pyriles passed into the acid state by means of 
its contact with the atmospheric air; and that this acid, com- 
bining with the argil, formed the crystals of alum.” . 
He repeated his observations, multiplied his experiments, and 
instituted more particular inquiries in the island, which led, he 
says, to a discovery of recent erystals formed from a decomposi- 
tion of the amorphous masses in which they were implanted. 
*< Nay, at one time, he seems to have caught nature in the very 
act of forming crystals of quartz on a mass of silico-calcareous 
earth, from the surface of which M. Methuon had carefully re- 
moved all signs of pre-existing crystallization. The author 
marked the spot well, and left it. After a few weeks, some small 
points of rock-crystal made their appearance; by degrees the 
pyramidal summits were formed ; and these were gradually fol- 
lowed by the prism; its mass diminishing in size, as the crystal 
became more and more diaphanous. At the end of three-and- 
twenty months, the period at which M. Methuon quitted the 
island, there were six beautiful crystals of quartz, from % to Z 
of an inch in length, and + of an inch in diameter ; the silico- 
calcareous stone around them being excavated in the same pro- 
portion. But a fluid seemed, in this instance, to have had a 
part in the formation of these crystals; for, although the locality 
of the fossil producing them is described to have been beyond: 
the reach of the waves, yet it is admitted that their spray, par- 
ticularly in tempestuous weather, often bedewed its exposed sur- 
face, | 
“In a similar manner did M. M. obtain crystals of -yenite, 
some specimens of which he has preserved to.this moment.” 
Afterwards 
