Yol.  49.] 
ST.  CASSIAN  STRATA  IN  SOUTHERN  TYROL. 
59 
These  faults  have  an  east-and-west  course,  and  extend  along  the 
whole  region  north  of  the  sunken  area.  If,  now,  the  strata  on  the 
southern  or  downthrow  side  be  brought  down  to  the  level  of  the  Men- 
dola  Dolomite  on  the  other  side  of  the  fault,  we  have  from  the 
Lower  Muschelkalk  a  continuous  outcrop  of  dolomite  up  to  the 
Raibl  strata. 
Loretz  has  previously  explained  this  as  in  part  the  result  of  such 
east-and-west  faults.  Mojsisovics,  on  the  other  hand,  has  explained 
it  as  an  unbroken  dolomitic  rock,  part  of  which  is  a  ‘  heteropic  ’ 
development  of  dolomite  corresponding  in  age  to  the  marls,  tuffs,  etc. 
of  the  St.  Cassian,  Wengen,  and  Buchenstein  periods. 
In  several  cases  I  found  that  the  younger  strata  were  brought 
down  by  faults  against  different  horizons  of  older  strata;  natu¬ 
rally,  in  the  particular  case  of  two  dolomitic  horizons  being 
faulted  against  one  another,  the  line  of  fault,  or  even  its  presence, 
is  extremely  difficult  to  prove,  not  only  from  the  lithological 
similarity  of  the  two  rocks,  but  also  from  their  poverty  in  fossils. 
One  of  the  main  fault-lines  recognized  by  Mojsisovics  (in  co¬ 
operation  with  the  survey  of  Hoernes)  is  the  Villnos  fault,  which, 
he  says,  may  be  traced  through  the  Villnos  Valley,  over  Campil, 
then  across  the  Enneberg  Valley,  through  Fanis,  south-east  to 
Peutelstein  and  towards  Tre  Croci.  I  could  not  convince  myself 
that  this  was  one  and  the  same  fault-line ;  for  instance,  Mojsisovics 
says  (op.  cit.  p.  293)  : — “  West  of  the  Wengen  Valley,  the  northern 
wing  of  the  fault-line  is  the  downthrow ;  east  of  the  Wengen  Valley, 
on  the  contrary,  it  is  the  southern  wing  which  is  the  downthrow.” 
So  far  as  my  own  observations  go,  the  Villnos  fault,  from  the 
Upper  Villnos  Valley  up  to  near  Campil,  belongs  to  the  set  of 
step-faults  already  mentioned,  which  have  thrown  down  the  older 
Triassic  strata  to  the  north.  That  part  of  the  Villnos  fault  which 
is  found  west  of  the  Enneberg  Valley  is  one  of  a  set  of  parallel 
faults  with  a  repeated  downthrow  to  the  south  occurring  within  the 
sunken  district  of  Dachstein  Dolomite. 
The  system  of  older  Triassic  rocks  faulted  up  both  east  and  west  of 
the  Groden  Pass  meets  farther  west  the  outer  zone  of  Werfen  Beds, 
Muschelkalk,  etc.  West  of  the  Tschisler  Alpe  and  Wolkenstein, 
therefore,  we  find  no  outcrop  of  Dachstein  Dolomite  and  younger 
Triassi  c  rocks,  the  Gardenazza  massif  and  Puez  forming  the  western 
limit  of  the  -  sunken  area.  Hence  it  is,  also,  that  the  relations  of 
the  strata  are  so  much  simpler  towards  Pufiatsch  and  Schlern. 
Two  of  the  districts  mapped  lie  in  the  southern  portion  of  the 
wide  area  just  discussed.  That  of  Prelongei  (Map  A)  is  precisely  on 
the  boundary-limit  where,  in  the  Buchenstein  Valley,  the  southern 
wing  of  the  broad  syncline  of  older  Trias  bends  up ;  that  of  Cortina 
(Map  B)  lies  just  south  of  the  area  of  subsidence,  below  the 
Dachstein  massif  of  Tofana.  But  the  map  of  the  Diirrenstein 
(Map  C)  lies  partly  in  the  outer  zone  of  older  Trias,  and  shows 
interesting  transitional  features  from  this  zone  to  the  Dachstein 
Dolomite. 
