|
GENESIS OF PEARLS
the
shell at the centre only, results. Two pearls held against the shell
and growing side by side are separately enveloped until they touch each
other, after which they are included in single deposits of nacre and
the depression between their domes becomes less distinct with each
successive coating. Similarly, a cluster of small pearls lying together
often forms the nucleus of a large rounded baroque or button pearl.
Examination of such formations shows, that up to a certain period the
pearls have a separate existence and growth. They then become joined in
an irregular mass of twinned pearls, and finally, if allowed to remain
in the oyster long enough, all individuality is lost in the tendency to
round over. The same thing occurs when grains of sand or other
intrusions become attached to a growing pearl. They are quite prominent
when first included in the nacreous deposit and can be easily detached
from the under pearl by breaking through the layer which binds them on;
but they are soon obliterated by succeeding deposits. This filling-in
process is sometimes accomplished by additional layers in the
depression, sometimes by thicker layers.
159
|
||
|
|
||