54 
THE PRINCIPAL FLOOR. 
originally made by the late Mr. Nevill, and purchased from him 
by Mr. Ludlam. This collection is here exhibited. 
Scientific attention was first seriously directed to the study of 
Meteorites about a century ago by the researches of the German 
physicist — Chladni. It is now usually believed that they are 
small cosmical bodies circulating in space, and brought from time 
to time within the sphere of the earth’s attraction. Many 
Meteorites have been seen to fall, but most specimens have been 
found as mineral masses on the surface of the earth, and have been 
regarded as meteoric in consequence of their peculiar composi- 
tion. Some are composed mainly of iron, and others of various 
stony silicates ; whence the common grouping of these bodies as 
meteoric irons and meteoric stones ; the 'general term meteorite 
being used to include both groups. 
The classification followed in arranging the meteorites in the 
Case is that adopted at the British Museum. Three groups are 
recognised ; 1 . Siderites * or Aerosiclerites, f consisting chiefly of 
metallic iron, usually alloyed with more or less nickel, and 
associated with such minerals as schreibersite (phosphide of 
nickel and iron), troilite (meteoric pyrites), graphite, &c. 
2. Siderolites,X which consist of a more or less continuous 
sponge-like mass of nickeliferous iron, having the cavities 
charged with various silicates, & c. 3. Aerolites ,§ or meteoric 
stones, consisting generally of one or more silicates, interspersed 
with isolated particles of nickel-iron, troilite, &c. 
Agates. Case No. 30. 
An agate is not a definite mineral, but rather an aggregate of 
various siliceous minerals, chiefly varieties of chalcedonic, jaspery 
and crystalline quartz. A large series of specimens, including 
some beautiful polished slabs, has been collected in this case. 
Some agates occur as veinstones, but by far the larger number 
are found in the cavities of certain igneous rocks, akin to basalt, 
but generally associated with palaeozoic strata. It is probable 
that the disengagement of gas or steam produced pear-shaped 
cavities in the igneous rock when in a fluid condition, and that 
these hollows, retained by the viscosity of the lava-like rock, 
have since been filled, partially or entirely, by silica and other 
substances deposited upon the walls of the cavities from solution 
in the water circulating through the rock. Many of the 
specimens in this case were selected by the late Prof. Noggerath, 
of Bonn, with the view of showing what he regarded as the 
inlets of infiltration through which the siliceous liquid may have 
gained access to the interior of the stone. Reference has 
already been made (p. 49) to the chief localities of agates and to 
the agate-industry which is centred at Oberstein. Most of the 
agates of commerce are now-a-days coloured by artificial jm> 
cesses, such as boiling them in oil or syrup, and subsequently 
* Greek ; sideros, iron. 
% Sideros. iron; lithos, stone. 
f Aer, air ; sideros , iron. 
§ Aer, air ; lithos , stone. 
