774 
SIE  ClIAELES  LTELL  OX  THE  STEI'CTUEE  OE  LAVAS 
Etna  was  a volcano  of  smaller  dimensions,  was  fii-st  overspread  with  allmium,  consisting 
of  well-rounded  pebbles  of  sandstone  and  other  non-volcanic  rocks,  intermixed  with  a few 
of  igneous  origin,  and  afterwards  oveidlowed  by  cuiTents  of  lava,  which  still  rest  on  the 
old  gravel.  The  superimposed  lavas,  often  imdely  columnar,  are  now  seen  running  out 
in  long  terraces  from  the  south-w'estern  base  of  the  great  cone,  and  ending  abniptly  in 
cliffs  which  face  the  valley  of  the  Simeto.  Thus,  for  example,  in  the  escarpment  facing 
south-west  between  Biancavilla  and  Licodia,  we  observe  above  the  fundamental  rocks  of 
sandstone  and  marl,  first,  a bed  of  pebbles  resting  unconformably  on  those  ancient  rocks ; 
and  2ndly,  the  incumbent  and  semi-columnar  dolerite. 
Passing  thence  by  Paterno  and  Misterbianco  to  Catania,  we  find  still  more  conclusive 
ewdence  that  the  ancient  littoral  and  delta-deposits  of  the  Simeto  and  its  tributaries  have 
been  upraised  to  very  considerable  heights  above  their  original  level,  by  movements  which 
have  also  elevated  the  subjacent  modern  tertiaries  in  the  country  called  the  Terra  Porte, 
south  and  west  of  Catania  (see  Map,  Plate  XLIX.).  These  same  tertiaries,  as  we  shall 
see  in  the  sequel,  also  crop  out  along  the  eastern  base  of  Etna,  and  contain  marine  shells, 
of  which  nearly  nineteen-twentieths  belong  to  species  still  living  in  the  Mediterranean. 
The  farther  we  recede  from  the  southern  foot  of  Etna  towards  the  channel  of  the  Simeto, 
the  more  dense  become  the  accumulations  of  upraised  pebbles.  At  Misterbianco,  which 
I visited  in  company  with  Signor  Geavina,  they  attain  a thickness  of  150  feet,  and  form 
the  capping  of  hills,  more  than  600  feet  above  the  sea-level.  They  are  entu’ely  different 
in  shape  and  composition  from  that  alluvium  of  exclusively  Etnean  origin,  with  angular 
fragments,  occurring  at  a a!  of  the  Map,  Plate  XLIX.,  for  they  consist  of  peiffectly 
rounded  pebbles  of  quartzose  grit,  nummulitic  limestone  and  sandstone,  fissile  clay- 
slates,  granite,  gneiss,  mica-schist,  and  a variety  of  other  rocks,  with  a very  moderate 
admixture  of  basalt*. 
Some  of  the  boulders  of  basalt,  and  some  of  those  composed  of  hard  tertiary  grits, 
are  o feet  and  upwards  in  diameter,  but  they  are  always  well-rounded.  They  have 
evidently  been  derived  from  rivers  which  drained  the  western  and  central  parts  of  Sicily, 
far  beyond  the  precincts  of  Etna.] 
[^Volcanic  erujjtions  in  the  alluvial  plain  of  the  Simeto. 
At  La  Motta  and  Paterno  we  find  within  the  area  of  the  ancient  estuary  some  highly 
interesting  monuments  of  local  volcanic  eruptions,  posterior  in  date  to  the  great  alhmum, 
for  they  have  cast  up  some  of  the  pebbles,  so  that  they  are  enveloped  in  tuff'  or  in  lava, 
and  often  much  burnt  and  altered.  At  La  Motta,  the  summit  of  a.  basaltic  and  tufa- 
ceous  hill  thus  formed  is  more  than  900  feet  high  above  the  sea.  The  sites  of  this  and 
of  other  local  outbreaks  in  the  same  region  are  well  laid  down  by  Hoffmaxx  in  his  Geo- 
logical Map  of  Sicily.  They  were  probably  coeval  with  the  earlier  suhaerial  eruptions 
of  the  cone  of  Etna  and  with  the  tuffs  of  Fasano,  of  which  I shall  presently  speak. 
I have  alluded  particularly  to  the  eruptions  of  La  Motta  and  Paterno,  because  as  they 
* See  a memoir  by  Signor  B.  Geaawna,  Bulletin  de  la  Societe  Geol.  de  Prance,  vol.  iv.  p.  403,  1S5S. 
