764 
SIE  CHAELES  LYELL  OY  THE  STELX’TUEE  OE  LAVAS 
two  hard  beds,  with  several  intervening  layers  of  a different  and  less  solid  composition.  In 
another  part  of  the  same  escarpment,  and  not  far  distant  in  the  upper  half  of  the  cliff,  the 
harder  beds  presented  the  irregularities  sketched  in  the  annexed  woodcut  (fig.  20),  the 
Fig.  20. — Non-parallel  strata  in  the  northern  escarpment  of  the  Val  del  Bove, 
to  the  south  of  Finocchio  Inferiore. 
Vertical  distance  from  a to  5 about  60  feet. 
aggregate  thickness  of  the  mass,  including  the  softer  intervening  beds,  being  about  60 
feet.  Between  perfect  parallelism  and  such  marked  de\iations  from  it,  as  are  here  indi- 
cated, there  is  every  intermediate  gradation. 
[In  the  higher  and  more  western  portion  of  the  same  escarpment,  called  the  Concazze 
(or  by  Abich  the  Cima  della  Valle),  where  the  stratification  has  been  described  as  very 
regular  and  parallel,  I distinctly  saw  a similar  thickening  and  thinning  out  of  the  beds 
as  viewed  from  the  rim  of  the  great  crater  of  1819,  the  want  of  parallelism  being  most 
conspicuous  in  the  upper  parts  of  the  precipice.] 
To  speak  next  of  the  southern  escarpment.  I may  first  remark,  that  when  a cliff  is 
between  1000  and  2000  feet  in  height,  like  the  Serra  del  Solfizio,  we  can  only  obtain  a 
general  view  of  its  hundreds  of  strata  by  placing  ourselves  at  a considerable  distance 
from  its  base ; in  which  case  all  the  minor  variations  in  dip  and  in  the  thickness  of 
individual  beds  may  escape  notice,  unless  specially  looked  for. 
M.  Abich  has  given  an  excellent  pictorial  representation  of  this  cliff  in  his  eighth  plate, 
taken  from  the  foot  of  Zoccolaro,  and  has  called  attention  to  the  general  uniformity  and 
regularity  of  the  lines  separating  the  numerous  beds.  But  even  in  the  Serra  del  Solfizio,  at 
certain  points  where  the  steep  cliffs  were  accessible,  and  where  we  measured  the  angles 
of  dip  and  the  thickness  of  the  beds,  we  invariably  found  the  appearance  of  strict  paral- 
lelism and  uniformity  of  stratification  to  vanish.  Before  adducing  particular'  examples, 
I may  observe  that,  besides  the  height  and  magnitude  of  the  section,  the  number  of 
dikes,  mostly  perpendicular,  but  some  of  them  having  a considerable  hade,  and  still  more 
the  numerous  ravines  which  have  been  excavated  by  torrents,  causing  gaps  from  150  to 
300  feet  in  width,  add  prodigiously  to  the  difficulty  of  tracing  a particular  bed  for  an 
indefinite  horizontal  distance.  The  gaps  alluded  to  cause  the  intervening  promontories 
of  rock  to  jut  out  like  the  side-scenes  in  a theatre  when  seen  in  profile,  as  is  well  repre- 
sented in  Abich’s  sketch  above  cited. 
At  the  first  point  where  we  tried  to  ascertain  whether  the  strata  were  persistent 
throughout  wide  spaces,  we  found  such  a want  of  correspondence  on  the  opposite  sides 
of  one  of  these  ravines,  that  we  began  to  suspect  that  we  had  at  length  discovered  a great 
