778 
SIE  CHAELES  LTELL  OX  THE  STEUCTHEE  OF  LAVAS 
Cyclopean  islands  do  now,  and  in  this  manner  we  may  explain  the  steep  cliffs  which 
they  present  in  every  direction,  some  facing  landward  and  others  seaward. 
In  order  to  understand  geographically  the  other  localities  where  the  tertiary  fossili- 
ferous  clays  crop  out  at  the  base  of  Etna,  we  must  return  to  Catania,  and  follow  the  coast 
which  trends  in  a north-east  direction  (see  Map,  Plate  XLIX.).  There  they  first  present 
themselves  at  Aci  CasteUo,  then  again  at  Trezza  opposite  the  Cyclopean  Isles,  and  again 
a mile  and  a half  north-west  of  that  place,  and  about  as  far  from  the  sea,  at  Xizzeti. 
At  all  these  points,  the  marine  clays  and  sands,  sometimes  reaching  elevations  between 
500  and  600  feet  above  the  sea,  are  associated  with  contemporaneous  basaltic  and  other 
igneous  products,  the  most  ancient  monuments  of  volcanic  eruptions  within  the  region 
of  Etna. 
During  my  first  visit  to  Sicily  in  the  year  1828,  I collected  at  two  of  the  above 
mentioned  localities  (Trezza  and  Nizzeti)  as  many  fossil  shells  as  I could  then  find,  and 
submitted  them  to  M.  Deshates  of  Paris,  who  referred  them  to  sixty-five  species,  the 
names  of  which  I published  in  the  Appendix  (p.  53)  to  the  third  volume  of  my  ‘Piin- 
ciples  of  Geology,’  which  appeared  in  1833.  I then  stated  (p.  79),  as  the  result  at 
which  the  eminent  French  conchologist  had  arrived,  “ that  almost  all  the  shells  were 
identical  with  species  now  inhabiting  the  Mediterranean,  and  for  the  most  part  now 
frequent  on  the  coast  immediately  adjacent.” 
A few  years  later  Dr.  Philippi  visited  Sicily,  and  in  his  ‘ Enumeratio  MoUuscorum 
Siciliee,’  published  in  1836,  gave  lists  of  the  shells  found  by  him  at  Nizzeti  and  Cefali. 
From  the  first  of  these  localities  he  obtained  seventy-six  species,  four  only  of  which  he 
regarded  as  extinct,  including  Murex  mginatus,  which  I have  now  ascertained  to  be 
a living  species.  In  his  list  of  109  shells  from  Cefali  he  marks  eight  as  extinct,  from 
which  also  we  must  deduct  Murex  mginatus^  so  that  according  to  his  investigations  the 
proportion  of  extinct  is  in  the  case  of  Nizzeti  only  four  in  the  hundred,  and  about  six 
in  the  case  of  Cefali. 
On  the  occasion  of  my  last  visits  to  Catania  in  1857  and  1858, 1 had  the  good  fortune 
to  make  the  acquaintance  of  Dr.  Aeadas,  an  eminent  physician  and  naturalist,  Avho 
possesses  the  finest  collection  yet  formed  of  the  Nizzeti  shells,  which  he  liberally  placed 
at  my  disposal,  allowing  me  to  take  them  to  Paris  and  London.  At  Paris  I obtained 
once  more,  after  an  interval  of  thirty  years,  the  kind  assistance  of  my  friend  M.  Deshates, 
in  determining  the  names  of  fossils  from  Mount  Etna,  consulting  him  especially  on 
points  on  which  Dr.  Aeadas  had  entertained  doubts.  With  one  or  two  corrections,  I 
have  printed  in  full,  in  the  Appendix  B,  p.  783,  this  list,  as  draAAUi  up  by  Dr.  Ailvd.as. 
He  has  indicated  therein  the  relative  abundance  of  each  species,  also  Avhich  of  them  are 
extinct,  or  not  at  present  known  in  the  Mediterranean.  The  total  number  of  species 
being  142,  sixty-seven  are  marked  as  additions  to  Philippi’s  list  from  the  same  place. 
Murex  vaginatus  was  given  as  extinct,  it  having  been  so  regarded  by  Philippi  ; but 
M.  Deshates  first  informed  me  (October  1858)  that  he  had  seen  a shell  fr’om  the  Medi- 
terranean, which  he  believed  to  be  identical,  and  Mr.  Cuming  has  since  shoAA  ii  me  three 
