WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
745 
Want  of  continuity  in  the  older  and  modern  parts  of  Mount  Etna,  and  truncation  of  the 
summit. 
The  evidence  on  which  some  writers  rely  in  proof  of  a discontinuity  of  the  operations 
which  produced  the  old  nucleus  of  Etna,  and  those  which  formed  the  more  modem 
portion  of  the  mountain,  seem  to  me  far  from  conclusive ; for  on  the  north-west,  the 
west,  and  part  of  the  south-west  sides,  there  may  have  been  a regular  and  almost 
uninterrupted  superposition  of  conformable  volcanic  products,  from  the  oldest  known 
trachytic  to  the  most  modern  doleritic  lavas 
S.  VON  Walteeshausen  has  shown  that  the  oldest  series  of  dikes  intersecting  the 
lavas  are  dioritic,  only  one  dike  of  trachyte  having  been  seen  by  him.  Next  to  the 
dioritic  or  greenstone  dikes  come  those  of  a kind  of  slaty  basalt,  to  which  he  gives  the 
name  of  phonolite,  while  the  third  and  last  series  consists  of  dolerites  and  greystones, 
or  “ trachi-dolerites.”  That  in  certain  parts  of  the  mountain  particular  sets  of  lavas 
should  be  found  resting  unconformably  on  other  and  older  rocks  was  to  be  expected,  as 
the  necessary  consequence  of  three  great  events  which  have  successively  worked  a change 
in  the  physical  geography  of  Etna ; namely,  first,  the  interference  of  the  products  of  the 
two  foci,  or  the  overflowing  of  Trifoglietto  by  the  newer  part  of  Mongibello,  as  before 
described  (fig.  15,  p.  740);  secondly,  the  truncation  of  the  summit  of  Mongibello,  to 
which  I shall  presently  advert ; and  thirdly,  an  event  in  part  perhaps  contemporaneous 
Pig.  17  . — Truncated  appearance  of  the  summit  of  Etna  on  the  north-west  side,  as  seen  from  near  Bronte,  from 
Saetoeixts  vox  Walteeshatjsex’s  Atlas,  plate  2. 
into  which  so  many  floods  of  lava  have  since  been  poured,  as  if  the  eruptive  powers 
* The  rock  here  called  trachyte,  is  so  designated  by  MM.  S.  v.Walteeshaesex  and  Abich,  as  it  appears 
to  me  with  propriety,  although  vox  Btich  considered  the  name  inappropriate,  because  the  felspar  he  says  is 
labradorite  and  not  glassy  felspar.  The  ordinary  appearance  of  the  felspar,  whether  in  the  older  or  newest 
lavas  of  Etna  (including  that  of  1852),  is  like  glassy  felspar,  so  far  as  having  the  same  vitreous  lustre.  The 
composition  of  the  mineral  in  the  trachytes  above  alluded  to  is  said  by  S.  v.  Waeteeshaesex  to  be  interme- 
diate between  labradorite  and  oligoclase.  Crystals  of  hornblende  and  of  augite  accompany  it,  but  no  quartz, 
— mica  very  rarely,  and  only  as  an  accidental  mineral. — S.  v.  Walteeshatjsex’s  Atlas,  V.  and  VI.  p.  3. 
5 E 2 
