390 SUPPLEMENT 
the great rivers of the north, and in many lakes. Those of the 
Tay, in Scotland, are in tolerable estimation. 
From what we have said concerning the origin and nature 
of pearls, it is evident that it must be very rare to find any 
which possess all the requisite qualities, that is, great regu- 
larity in form, whether that be round, oval, or pear-shaped ; 
a fine water, or a tint white, lively, with brilliant reflections, 
similar to those of the opal, which is called a fine Orient, and 
finally, a considerable bulk. Accordingly, those which combine 
all these qualities are of an excessive price, and it requires 
some art in the jeweller to unite, in the formation of a neck- 
lace, or any other ornament, pearls which are well matched 
in size, and still more in tint or colour. 
The irregular pearls are termed, in commercial language, 
uneven, and those which are extremely small, and seldom 
very regular, are called seed pearls. 
The pearls of Europe, or the Union pearls, are sometimes 
very fine and rather large. But the majority have little or no 
brilliancy. They are found of all forms. 
Pearls are of different colours; most generally they are 
white and nacreous, but sometimes they are yellowish, or 
greenish, or even livid or lead-coloured. Tavernier informs 
us that he had six in his possession that were jet-black. It 
is supposed that these colours are owing either to the pearl 
having remained too long in the putrified animal, or perhaps 
to the latter having lived in mud which was more or less 
fetid. : 
The jewellers sometimes make very large ones, but which 
are composed of two knobs of pearl applied one upon the 
other; these are only hemispherical tubercles, rounded, and 
which have been taken from the interior of a pearly shell. 
Pearls have the great disadvantage of changing, and being 
deteriorated by time. They more especially alter quickly 
when worn immediately upon the skin. They tarnish and 
