I02 Pearls. 



Lower Silurian period, if not earlier, and they have 

 not only held their own, but have gradually in- 

 creased in number and variety of type, up to the 

 present day. The family oi Aviciilidcs flourished in the 

 Carboniferous period, and beds containing immense 

 numbers of Avicula Contorta occur in the Triassic 

 or Rhoetic series, in the Austrian Alps. The more 

 interesting Gasteropods and Cephalopods also have 

 their histories clearly marked out from a very early 

 date. Bivalves have undoubtedly been most suc- 

 cessful in the struggle for existence, and this power 

 may be partly attributed to their ability of closing 

 their shells when attacked, and presenting an im- 

 penetrable front of " masterly inactivity.'* 



It is needless to enumerate the articles for the 

 manufacture of which Pearl shell is sought after. 

 For buttons and studs, for knife-handles, card-cases, 

 and for ornamental work generally, Mother-of-Pearl 

 has no rival. Its adoption is of no modern date, 

 articles of this substance liaving been discovered 

 in the excavations at Nineveh and Babylon. 



One important application of Mother-of-Pearl 

 is that of hafting cutlery, especially fruit knives 

 and pocket knives. The two flat plates of shell, 

 which are rivetted to the central part of the handle, 

 are technically termed "scales," and these require to 

 be tediously ground down and polished by hand. 



