Vol.  49.]  ST.  CASSIAN  STRATA  IN  SOUTHERN  TYROL.  77 
St.  Cassian  strata  and  overlying  dolomite  repeatedly  to  tlie  south,  so 
that,  although  a  comparatively  small  thickness  of  St.  Cassian  strata 
is  exposed  on  the  Alpe,  their  outcrop  continues  very  nearly  as  far 
as  Schluderbach.  Then,  however,  the  north-and-south  fault  has  on 
the  western  or  downthrow  side  Dachstein  Dolomite,  and  on  the 
eastern  or  upthrow  side  the  Schlern  Dolomite  of  Strudelkopf  and  of 
Monte  Pian  farther  south. 
The  most  important  tectonic  relation  is  that  brought  out  by  the 
north-west  and  south-east  fault  which  separates  the  Diirrenstein 
massif  from  the  4  Dachstein  Dolomite  region  ’  of  Rauhe  Gaisl, 
Schlecht  Gaisl,  and  Hohe  Gaisl  (Croda  Rossa).  These  form  part  of 
the  sunken  area  west  of  the  Diirrenstein.  The  Knollenkopf  is  a 
mass  of  Dachstein  rock,  let  down  between  two  branches  of  this 
main  fault,  the  westerly  branch  passing  through  the  Knappenfuss 
Valley. 
Downthrow  of  the  strata  has  taken  place  also  on  the  eastern  side 
of  the  Diirrenstein.  The  Sari  Brand,  as  already  mentioned,  is  sunk 
from  the  Sari  Kofi,  and  the  Muschelkalk  faulted  down  ;  the  Nock- 
boden  is  sunk  from  Kasamiitz  and  the  Sari  Alp ;  and  towards 
Landro  the  eastern  part  of  the  Diirrenstein  is  sunk  from  the  main 
ridge.  By  this  north-and-south  fault  through  the  Diirrenstein,  an 
apparently  much  greater  thickness  of  Schlern  Dolomite  is  seen 
above  the  Toblach  Valley  than  on  the  northern  or  western  sides. 
No  part  of  this  thickness  is  due  to  Mendola  Dolomite,  as,  for 
instance,  is  the  case  south  of  Schlern  ;  in  the  Diirrenstein  massif \ 
the  only  place  where  Mendola  Dolomite  underlies  Schlern  Dolomite 
is  at  Nockboden. 
We  have,  therefore,  sunken  massifs  both  west  and  east  of  the 
Diirrenstein  ;  that  mountain  itself  remains  at  a  higher  level 
between  the  two,  and  may  be  called  a  4  Horst  ’  in  the  sense 
originally  applied  by  Suess.1  At  the  same  time  the  4  Diirrenstein 
Horst’  borders  on  the  4  Dachstein  ’ region,  and  this* nearness  to  the 
important  fault  finds  expression,  especially  on  the  western  side,  in  a 
number  of  smaller  faults. 
In  the  Platz  Wiese  system,  the  strata  are  sunk  much  lower  in 
the  south-western  portion  near  the  4  Dachstein  ’  region  than  in  the 
eastern  or  Diirrenstein-ridge  portion,  and  in  the  Strudelkopf  system 
we  find  repeated  sinking  of  the  strata  southward,  towards  the 
Dachstein  Dolomite  massif  of  Monte  Cristallo. 
Discussion. 
Mr.  J.  W.  Gregory  remarked  on  the  many  questions  of  interest 
which  this  paper  affected.  The  Authoress’s  work  had  destroyed  faith 
in  the  most  famous  fossil  atoll,  doubts  as  to  wrhich  had  been  pre¬ 
viously  suggested  by  palaeontological  and  stratigraphical  considera¬ 
tions.  Careful  zonal  collecting  in  these  beds  was  greatly  needed,  as 
in  the  three  principal  collections  (Vienna,  Munich,  and  London) 
the  fossils  are  simply  localized  as  St.  Cassian.  The  fauna,  with  its 
1  ‘  Antlitz  der  Erde.’  1st  ed.  1885,  vol.  i.  p.  167. 
