WHICH  HA^"E  CONSOLIDATED  ON  STEEP  SLOPES. 
705 
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Age  of  the  marine  tertiary  strata  of  Cefali,  Nizzeti,  and  Catira  777 
Modern  date  of  the  mass  of  Etna  780 
Eecapitulation  of  Part  III.,  and  concluding  remarks  on  the  theory  of  “ Craters-of- 
elevation  ” 781 
Appendix. 
A.  Description  of  fossil  plants  from  the  volcanic  tuff  of  Fasano  near  Catania,  by 
Professor  Oswald  Heee 782 
B.  List  of  fossil  shells  from  the  Newer  Pliocene  of  Nizzeti,  by  Professor  Andeea 
Aeadas,  of  Catania  783 
C.  List  of  fossil  shells  and  Echinoderms  from  Catira,  near  Catania,  by  Signor 
Gaetako  G.  Gemmellaeo 786 
PART  I. 
ON  THE  STEUCTHEE  OF  MODEEN  LAVAS  WHICH  HAVE  CONGEALED  ON  STEEP 
SLOPES. 
Preliminary  remarks  on  the  characters  commonly  attributed  to  lavas  ivhich  have  consoli- 
dated on  steep  slopes,  and  on  the  theory  of  Craters  of  Elevation^ 
The  question  whether  tabular  masses  of  lava  having  a compact  and  stony  texture,  and 
a thickness  of  many  feet,  can  be  formed  on  slopes  inclined  at  angles  of  from  10°  to  40°, 
has  of  late  years  acquAed  considerable  importance,  since  geologists  of  high  authority 
have  assumed  that  if  the  inclination  exceed  5°  or  6°,  a lava-current  will  be  scoriaceous 
in  texture,  fragmentary  in  structure,  and  insignificant  in  thickness.  Such  steeply- 
inclined  currents,  it  is  said,  can  never  give  rise  to  beds  of  compact  rock,  comparable  to 
those  solid  layers  which  we  see,  alternating  with  scorite  and  tuff,  in  the  older  parts  of 
volcanic  mountains,  such  as  the  escarpments  of  Somma  in  the  case  of  Vesuvius,  or  the 
cliffs  surrounding  the  Val  del  Bove  in  the  case  of  Etna. 
It  has  even  been  laid  down  as  a rule  by  one  geologist  of  eminence,  the  late  M.  Du- 
FRESNOT  of  Paris,  that  lavas,  to  be  compact  and  crystalline,  must  have  consolidated  on  a 
slope  not  exceeding  1°  or  2°.  He  states,  in  his  memoir  on  “ Vesuvius  and  its  Environs  ” 
(1834),  “ Les  laves  ne  sont  compactes  et  cristallines  que  lorsqu’elles  se  sont  repandues  sur 
un  sol  ayant  1 degre  a 2 degres  au  plus  d’inclinaison Lorsque  la  pente  du  terrain 
est  superieure  a 2°  la  texture  compacte  commence  a s’effacer,  les  laves  deviennent  bul- 
leuses  et  meme  scoriacees.  Les  coulees,  qui  se  presentent  sous  un  angle  de  4°  ne  sont 
plus  que  des  agglomerations  de  fragments  incoherents*.”  M.  Elie  de  Beaumont,  in  his 
* “ Terrains  volcaniques  des  environs  de  Naples,”  Mem.  pour  servir  a une  description  geol.  de  France, 
tome  iv.  p.  342. 
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