WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
749 
ably,  were  brought  into  their  present  position  by  mechanical  forces  after  the  materials 
of  the  mountain  had  accumulated  on  nearly  level  ground. 
It  has  been  suggested  by  M.  Elie  de  Beaumont,  that  when  (as  during  the  eruption  of 
1832)  new  fissures  are  produced,  radiating  from  the  centre,  and  traversing  the  nucleus  of 
Etna,  and  when  lava,  after  rising  simultaneously  to  the  rim  of  the  highest  crater,  has  filled 
such  fissures,  there  may  result  an  upheaval  of  the  whole  cone,  and  in  this  way  the  tume- 
faction or  distension  of  the  mass  may  have  been  going  on.  He  even  thinks  that  the  cone 
may  acquire  as  much  height  by  this  machinery  as  by  the  accession  of  new  external  coats 
of  lava. 
I may  first  be  allowed  to  remark,  that  if  such  a doctrine  be  embraced,  it  would  help 
us  to  dispense  with  that  paroxysmal  violence  or  grand  terminal  catastrophe  which  holds 
so  prominent  a place  in  the  “ crater-of-elevation  ” hypothesis. 
eg  [Unfortunately  we  have  at  present  no  data  for  deciding  whether  the  dike-making 
process  thus  appealed  to  is  usually  attended  by  upheaval.  That  on  some  occasions  it 
indicates  a collapse  and  partial  subsidence  of  the  flank  of  the  cone  in  such  a manner  as 
might  either  increase  or  diminish  the  angle  of  dip,  seems  proved  by  the  observations  of 
ScACCHi  on  Vesuvius  in  1850  and  1855,  and  by  those  of  Julius  Schmidt  in  1855.  The 
last-mentioned  observer  looked  in  vain,  in  the  walls  of  the  long  cavity  caused  by  subsi- 
dence (and  in  which  probably  a new  dike  was  forming  by  injection  of  lava  into  the  flanks 
of  the  cone),  for  signs  of  upheaval*. 
That  an  uplifting  of  the  incumbent  mass  must  accompany  the  injection  of  liquid 
matter  through  fissures  which  are  not  perpendicular,  some  of  which,  as  I saw  in  the 
Serra  Intermedia,  are  inclined  at  an  angle  of  75°  to  the  horizon,  no  one  can  deny.  Such 
injected  rents,  when  very  wide,  must  modify  greatly  the  position  of  the  overlying  and 
intersected  beds,  both  in  a horizontal  and  vertical  direction.  S.  von  Walteeshausen, 
therefore,  while  rejecting  the  hypothesis  of  a single  terminal  catastrophe,  or  any  paroxys- 
mal development  of  the  elevating  force,  ascribes  no  small  influence  to  those  disturbing 
operations,  by  which  such  innumerable  dikes  have  been  formed  near  the  principal  centres 
of  eruption. ]g3 
The  same  author,  who  has  studied  Etna  for  a longer  time  and  more  attentively  than 
any  other  geologist,  supposes  the  volcano  to  have  assumed  its  present  form  and  dimen- 
sions gradually  by  the  joint  effect  of  the  overflowing  of  lava  and  the  injection  of  the 
same,  not  only  into  vertical  fissures,  but  in  sheets  parallel  to  the  previously  deposited 
tuffs  and  lavas.  By  these  intercalated  and  conformably  intruded  masses,  according  to 
him,  much  elevation  has  been  brought  about,  an  hypothesis  to  the  discussion  of  which  I 
shall  presently  return.  The  great  point  to  be  chiefly  kept  in  view  in  the  present 
memoir,  is  simply  whether  the  quaquaversal  arrangement  of  the  beds,  in  cones  like  Etna 
and  Somma,  and  the  high  inclination  of  the  lavas  and  scoriae,  are  not  mainly,  and  in 
many  cases  exclusively,  due  to  eruption,  and  whether  the  upheaving  power,  even  grant- 
ing its  intervention,  does  not  play  a very  subordinate  part.  On  this  head  we  may  con- 
* Die  Eruption  des  Vesuy  im  1855,  p.  44.  (Wien,  1856.) 
