er which the stratum of rock had been originally
deposited. These earths are generally of a white or grey colour. Some of
them are hard, but most are soft and friable. Many of them are of
economic importance, being used as polishing powders ("Tripoli"), as
absorbents for nitroglycerin in the manufacture of dynamite
("Kieselguhr"), as a dentifrice, and more recently they have been used
to a large extent in the manufacture of non-conducting and sound-proof
materials. Most of these diatomaceous earths are associated with rocks
of Tertiary formations, although it is generally regarded that the
earliest appearance of diatoms is in the Upper Cretaceous (chalk).

Vast deposits of Diatomaceous earths have been discovered in various
parts of the world,--some the deposit of fresh, others of salt water. Of
these deposits the most remarkable for extent, as well as for the number
and beauty of the species contained in it, is that of Richmond, in
Virginia, one of the United States of America. It extends for many
miles, and is in some places at least 40 ft. deep. It is a remarkable
fact that though the generations of a diatom in the space of a few
months far exceed in number the generation of man during the period
usually assigned to the existence of the race, the fossil genera and
species are in most respects to the most minute details identical with
the numerous living representatives of their class.
(E. O'M.; G. S. W.*)

DIAULOS (from Gr. [Greek: di-], double, and [Greek: aulos], pipe), in
architecture, the peristyle round the great court of the palaestra,
described by Vitruvius (v. II), which measured two stadia (1200 ft.) in
length; on the south side this peristyle had two rows of columns, so
that in stormy weather the rain might not be driven into the inner part.
The word was also used in ancient Greece for a foot-race of twice the
usual length.

DIAVOLO, FRA (1771-1806), the popular name given to a famous Italian
brigand associated with the political revolutions of southern Italy at
the time of the French invasion. His real name was Michele Pezza, and he
was born of low parentage at Itri; he had committed many murders and
robberies in the Terra di Lavoro, but by good luck combined with
audacity he always escaped capture, whence his name of Fra Diavolo,
popular superstition having invested him with the characters of a monk
and a demon, and it seems that at one time he actually was a monk. When
the kingdom of