Vol.  49-] 
ST.  CASSIAN  STRATA  IN  SOUTHERN  TYROL. 
3 
The  Muschelkalk  is  succeeded  in  Southern  Tyrol  sometimes  by 
an  immense  thickness  of  dolomitic  rock,  poor  in  fossils,  sometimes  by 
a  non -dolomitic  series  of  strata.  The  lowest  of  the  non-dolomitic 
series  are  the  Buchenstein  Beds,  a  series  of  shales  and  limestones 
comparatively  poor  in  fossils,  but  indicative  of  shallow-water  con¬ 
ditions  ;  next,  a  group  known  as  the  Wengen  strata,  consisting  of 
sandstones  and  shales,  formed  apparently  more  or  less  by  the  wash¬ 
ings  of  volcanic  (sub-basic)  material,  and  known  usually  as  ‘  sedi¬ 
mentary  tuffs.’  These  are  cut  through  by  augitic  porphyry-dykes, 
or  are  interrupted  at  various  horizons  by  flows  of  augite-porphyry, 
with  volcanic  tuffs.  The  sedimentary  beds  are  fossil-bearing,  and 
while  the  species  are  few,  the  individuals  are  numerous. 
Next  follow  the  most  celebrated  beds  of  the  whole  Triassic  series, 
the  marls  and  limestone-rocks  of  St.  Cassian,  which  afford  that 
curious  mixture  of  older  forms  of  life,  as  yet  almost  unique  in  the 
geological  world. 
Above  the  St.  Cassian  Beds,  according  to  one  opinion,  follow  at 
once  the  fossil-bearing  Baibl  Beds ;  in  Southern  Tyrol  these  are 
especially  characterized  by  the  brilliant  colouring  of  the  reddish  and 
violet  marls,  which  are  interstratified  with  dolomitic  flags  in  the 
upper  horizons.  According  to  another  opinion,  there  is  between 
the  fossiliferous  St.  Cassian  and  the  fossiliferous  Baibl  Beds  a 
distinct  horizon,  formed  by  the  same  Schlern  Dolomite  as  that 
which  extends  in  some  localities  in  Southern  Tyrol  from  the  Baibl 
Beds  above  to  the  Muschelkalk  below. 
The  Dachstein  Dolomite  succeeds  the  Baibl  Beds  in  all  cases,  and 
above  the  whole  Triassic  series  follow  the  acknowledged  Liassic 
strata. 
The  difficulty  in  Southern  Tyrol  arises  in  the  anomalies  presented 
by  those  beds  which  are  above  the  Muschelkalk  and  below  the 
Baibl  strata.  The  dolomitic  rock  thickens  out  locally  into  moun¬ 
tain-masses  or  is  suddenly  replaced  by  shales.  The  very  fossili¬ 
ferous  beds  of  one  locality  are  represented,  a  few  miles  off,  .by 
strata  wholly  barren  of  organic  remains. 
As  yet.  comparison  with  the  ascertained  succession  in  Northern 
Tyrol  lends  little  help.  In  Northern  Tyrol,  the  Baibl  Beds,  as  a 
series  of  marls  and  oolitic  limestones  often  richly  fossiliferous,  and 
interbedded  with  unfossiliferous  dolomite,  limestone,  and  gypsum, 
rest  upon  the  thick  development  of  limestone  known  as  Wetterstein 
Balk.  This  limestone  is  generally  regarded  as  the  representative 
of  the  dolomitic  rock  below  the  Baibl  Beds  in  Southern  Tyrol. 
Below  the  Wetterstein  Balk  and  above  the  Muschelkalk  are  the  Part- 
nach  strata,  a  series  of  dark  thin-bedded  shales  which  von  Giimbel, 
von  Hauer,  and  others  have  compared  with  the  Wengen  strata  of 
Southern  Tyrol,  owing  to  the  identity  of  some  characteristic  fossils, 
A  g.  Halobia  Lommeli ,  Wissm. 
Thick  beds  of  hard  limestone  are  interstratified  at  various  horizons 
n  the  Partnach  shales  and  marls,  and  such  limestones  bear  typical 
it.  Cassian  fossils,  e.  g.  Koninckina  Leonhardti ,  Wissm.,  and  have 
lence  been  called  4  St.  Cassian  limestones.’  Several  of  the  species 
b  2 
