26 FIELD CoLuMBIAN MusrEuM—GEOLocy, VOL. 1. 
In specific gravity the majority of aerolites range from 3.00 to 
3.80, being on the whole heavier than terrestrial rocks of the same 
nature on account of the greater quantity of metallic constituents. 
Viewed as to structure the greater number of aerolites are found 
to be made up chiefly of little spheres, varying in size from those as 
large as a cherry to those only visible under the microscope. These 
are called chondri from the Greek yovdpos, a bail, and meteorites pos- 
sessing this structure are said to be chond ttic. 
The chondritic structure is often discernible by the naked eye, as 
may be seen in the specimens of Weston (224), Forsyth (240), Pusi- 
nsko (250), Trenzano (268), Knyahinya (284) and many others. 
When examined with sufficient magnifying power the chondri 
can be seen to be composed of angular, crystalline fragments chiefly 
of chrysolite or some pyroxene. See Plate VI, Fig,1. These may be 
present as one individual (monosomatic) or more commonly of several 
(polysomatic). 
An eccentric fan-shaped chondrus made up of radiating fibres 
- of enstatite is a very unique and characteristic form. One such may 
be noted in the section of the Simbirsk meteorite, shown in Plate VI, 
Fig. 1. Other arrangements of the grains or fibres which st bé 
noted are concentric, reticulated and radiated. 
The chondrus is frequently enclosed in a shell of metallic grains 
which gives it a distinct outline and separates it from the ground mass. 
This is illustrated in Plate VI, Fig. 2. 
The conditions which have brought about the formation of these 
chondri are not well understood though the question has been much 
discussed and various hypotheses have been suggested. The views 
of earlier observers were to the effect that the chondri represented 
fragments of pre-existing rock which by oscillation and consequent 
attrition obtained a spherical form. Sorby* has regarded them as 
produced by cooling and aggregation of minute drops of melted 
stony matter. Tschermakt considers their origin similar to that of the 
spherules met with in volcanic tuffs, which owe their form to pro- 
longed explosive activity in a volcanic throat, breaking up the older 
rocks and rounding the particles by constant attrition. 
Different views are, however, set forth by Brezina{f and Wads- 
worth§, who believe that the chondri have been produced by rapid 
and arrested crystallization in a molten mass. 
*Geol. Mag. 1865 (1) ii, 447. 
+Phil. Mag. 1876 (5) i, 497-507. 
{Die Meteoritensammlung in Wien, 1885, p. 19. 
§Lithological Studies, p. rio, 
