782 
SIE  CHAELES  LTELL  ON  THE  STEUCTTEE  OF  LAVAS 
remains  to  be  worked  out  is,  how  far  each  mountain  of  igneous  origin,  whether  having 
a double  axis  like  Etna,  or  a single  one  like  Vesuvius,  may  owe  a part  of  its  conical  or 
dome-like  form  to  a gradual  distension  of  the  mass  brought  about  by  the  injection  into 
it  of  many,  and  sometimes  voluminous,  dikes  of  melted  matter ; also  how  far  the  same 
agency  may  impart  to  the  tufiFs  and  lavas  a steeper  inclination  than  that  which  they  had 
originally.  The  answer  to  such  inquiries  may  perhaps  be  different  in  each  separate  cone ; 
but  whether  one-fifth  of  the  inclination,  as  I have  suggested  as  possible  in  the  case  of 
Etna,  or  a greater  or  less  amount  be  ascribable  to  this  cause,  I have  come  to  the  con- 
viction that  upheaval  has  nowhere  played  such  a dominant  part  in  the  cone  and  crater- 
making  process,  as  to  warrant  the  use  of  the  term  “ elevation-craters,”  instead  of  cones 
and  craters  of  eruption.  Such  a designation,  as  well  as  the  theory  imphed  by  it,  would 
be  alike  inappropriate  in  the  case  of  all  the  igneous  mountains  which  I have  seen, 
whether  in  Sicily  or  the  Phlegrean  Fields,  or  in  the  volcanic  district  of  Rome  or  that  of 
Central  France,  or  lastly,  of  Madeira  and  the  Canaries. 
APPENDIX.— A. 
Remaeks  on  the  Fossil  Plants  feom  the  Volcanic  Tuff  of  Fasano  neae.  Catanlv  on 
Mount  Etna,  extracted  from  a letter  addressed  to  the  author  by  Professor  Oswald 
Heee,  of  Zurich,  dated  April  1858. 
The  leaves  from  the  volcanic  tuff  of  Etna  belong  to  three  species  now  h’^ing  in  Sicily, 
namely,  Laurus  nobilis,  L.,  Myrtus  communis,  L.,  and  Pistacia  lentiscus,  L. : the  mp-tles 
and  laurel  leaves  are  the  commonest,  and  are  probably  those  which  you  mention  as 
having  been  mistaken  for  those  of  Quercus  ilex,  L. 
Desceiption  of  the  species. 
1.  Laurus  nobilis,  L.,  fig.  3,  Plate  LI. — Several  leaves,  exactly  agreeing  ndth  the 
living  species.  Leathery  leaves,  narrowing  at  the  base  into  the  leaf-stalk,  border  entire 
or  sometimes  wavy,  the  secondary  nerves  arched,  the  bodies  of  the  leaves  filled  with  a 
distinct  network. 
Easily  to  be  distinguished  from  Quercus  ilex  by  the  narrowed  base  towards  the  leaf- 
stalk and  the  nervation. 
2.  Myrtus  communis,  L.,  figs.  4 and  5,  Plate  LI. — The  most  numerous  of  the  leaves 
from  Fasano.  They  have  completely  the  characteristic  nervation  of  mptle  leaves,  a 
distinct  border  nerve,  which  runs  parallel  to  the  edge,  and  receives  the  numerous  deli- 
cate secondary  nerves.  Here  and  there  the  nervillae  may  also  be  detected.  The  second- 
ary nerves  appear  to  be  rather  more  numerous  than  in  the  liHng  myrtle. 
There  are  two  principal  divisions : — 
a.  Fig.  4,  Plate  LI. — Leaves  agreeing  in  size  and  form  with  the  lal•ge-lea^■ed  myrtle 
of  Italy  and  of  our  greenhouses.  They  are  also  pointed  at  the  end. 
b.  Fig.  5,  Plate  LI. — The  others,  on  the  contrary,  are  much  larger,  and  sometimes 
blunt  at  the  end,  such  as  are  found  in  myrtles  kept  in  greenhouses  and  wet  soils.  But 
