1877.] Microscopy. 187 
rich in fossils. At a much higher level we have the gypsum of Aix, 
which you probably know by name at least. 
I beg you will accept my highest regard and sincere devotedness. — 
Count GASTON DE SAPORTA, Aix in Provence. 
MICROSCOPY.! 
Microscopical STRUCTURE OF AmMBER.— A paper on this subject, 
contributed jointly by H. C. Sorby and P. J. Butler, to the Royal Mi- 
croscopical Society, furnishes many interesting observations and reflec- 
tions. Scattered irregularly through the masses of amber are a vast 
number of minute cavities, usually syy to s9}p9 of an inch in diameter, 
though some are as large as qyp, and others probably as small as 
rodses Of an inch. Though very numerous in the clouded portions of 
the amber, these cavities are nearly wanting in the very transparent 
specimens, and therefore cannot be considered a necessary result of the 
changes which occurred during the hardening of the balsam or resin from 
which the amber must have been formed. They are usually round, the 
shape which would be naturally assumed by drops of water or bubbles of 
air confined in a stiff liquid, differing in this respect from the cavities in 
crystals which are often spaces left vacant during the formation of the 
crystal, and are bounded by crystalline planes having direct relation to 
the form and structure of the crystal itself. The cavities in amber, how- 
ever, are sometimes elongated or otherwise changed by internal move- 
ments in the resinous mass before it became hard and brittle. Some of 
these cavities are filled with a liquid, probably water, which differs so 
slightly from the amber in refractive power, that these cavities are trans- 
parent throughout a large portion of their area, the circumference being 
marked by a narrow, dark line. Other cavities contain gas, constituting 
true air bubbles, whose dark outline constitutes at least one third of their 
diameter, leaving a comparatively small bright spot in the centre. Still 
other cavities contain liquid with an inclosed air bubble ; while some of 
the fluid cavities only seem to contain one or more air bubbles from the 
appearance through them of images of one or more smaller cavities be- 
neath. Most of the cavities originally contained water, which was elim- 
inated during the process of change from a soft balsam to a hard resin, 
but subsequently the water escaped from many of the cavities leaving 
air cavities instead, which are not only especially abundant near the 
natural surface of pieces of amber, but may also be found very generally 
Close to the surfaces of sections which have been prepared and mounted 
for microscopical use. A comparatively rare form ôf cavity, and charac- 
teristic of amber, is balloon shaped, the portion representing the car be- 
ing nearly always filled with water and the upper part of the balloon 
with air. This may have been originally a round fluid cavity, from 
Which the gas was allowed to escape into the still plastic, surrounding 
1 Conducted by Dr. R. H. Warp, Troy, Nr 
