780 
SIR  CHAELES  LTELL  01s  THE  STEUCTTEE  OE  LAVAS 
remain  57  species,  of  which  five  are  extinct;  a proportion  of  about  9 per  cent.,  implying 
a somewhat  greater  divergence  from  the  recent  fauna  than  the  other  lists.  One  also  of 
the  three  echinoderms,  Brissus  cylindricus^  is  only  known  as  fossil;  but  as  I have  had 
no  opportunity,  aided  by  skilful  conchologists,  of  comparing  the  fossils  themselves 
named  in  this  list  with  the  large  collections  in  the  Museums  of  Paris  and  London,  I 
am  not  sure  that  the  Catira  fossils,  if  subjected  to  a similar  scrutiny,  would  not  yield 
results  in  more  exact  harmony  with  those  obtained  from  other  localities.  Signor  Gem- 
MELLAEO  himself  stated  to  me,  that  not  only  do  the  majority  of  the  Catira  shells  agree 
specifically  with  those  now  hving  in  the  Sicihan  seas,  but  the  mdi-siduals  are  of  the 
same  average  size  and  aspect,  which  is  not  the  case  with  those  foimd  fossil  in  some  of 
the  older  tertiary  formations  in  Sicily. 
Modern  date  of  the  mass  of  Etna. 
If  asked  to  which  of  our  British  tertiary  strata  those  of  Nizzeti  and  Cefah  approach 
most  nearly  in  age,  I have  no  hesitation  in  answering,  the  Norwich  Crag;  but  the 
latter  formation  is  probably  the  older  of  the  two,  its  fossils  appealing  to  diverge  some- 
what further  from  the  fauna  of  our  British  seas,  than  do  the  shells  of  the  Etnean  locah- 
ties  above  mentioned  from  the  mollusca  now  inhabiting  the  Mediterranean.  If  so,  the 
great  mass  of  Etna,  or  all  that  is  of  subaerial  origin,  being  newer  than  the  Nizzeti  clays, 
must  be,  geologically  speaking,  of  extremely  modern  date.  Its  foundations  were  pro- 
bably laid  in  the  sea;  and  were  in  all  likelihood  contemporaneous  with  the  basalts  and 
other  igneous  products  of  the  Cyclopean  Isles  and  Aci  Gastello,  which,  as  we  have 
stated,  belong  to  the  period  of  the  fossil  shells  of  Nizzeti  and  Cefah.  AATien  that  fauna 
flourished,  the  area  where  Etna  now  rises  was  probably  a bay  of  the  sea,  afterwards 
converted  into  land  by  the  outpouring  of  lava  and  scoriae,  as  well  as  by  the  slow  and 
simultaneous  upheaval  of  the  whole  territory.  During  that  gradual  rise  the  ancient 
river-plain  of  the  Simeto,  in  which  were  imbedded  the  remains  of  the  elephant  and 
other  quadrupeds,  together  with  certain  marine  strata  (those  of  Camuhu)  formed  near 
the  mouth  of  that  river,  acquired  their  present  comparatively  elevated  position.  The 
local  eruptions  of  La  Motta  and  Paterno  took  place  about  the  same  time,  i.  e.  dming  or 
immediately  after  the  deposition  of  the  older  alluvium,  when  also  the  leaf-beaiing  tuffs 
of  Fasano  were  formed.  In  the  course  of  the  same  long  period  of  elevation,  the  cone 
of  Trifoglietto,  and  probably  the  lower  part  of  the  cone  of  Mongibello,  were  built  up. 
Still  later  the  cone  last  mentioned,  becoming  the  sole  centre  of  actmty,  oveiAvlielmed 
the  eastern  cone,  and  finally  underwent  in  itself  various  transformations,  including  the 
truncation  of  its  summit  and  the  formation  of  the  Val  del  Bove  on  its  eastern  flank. 
At  length  the  phase  of  lateral  eruptions,  which  is  still  in  full  vigour,  closed  this  long 
succession  of  events — changes  which  may  have  requhed  thousands  of  centuiies  for  then 
development,  although  in  the  same  lapse  of  time  the  molluscous  fauna  of  the  Mediter- 
ranean has  scarcely  undergone  a twentieth  part  of  one  enthe  revolution. 
We  have  seen  that  almost  all  the  common  shells  of  Nizzeti  are  of  Ihing  species;  but 
this  is  still  more  true  of  the  fossil  shells  of  the  glacial  epoch  in  Northern  Europe  and 
