178  PROF.  J.  W.  JUDD  ON  INCLUSIONS  OF  TERTIARY  [May  1 893, 
from  E.  Neumann,  an  optician  in  that  town,  who  was  one  of  the 
earliest  makers  of  microscopic  slices  of  minerals  and  rocks,  a  thin 
section  which  at  the  time  arrested  my  attention  and  has  often 
since  been  referred  to  with  interest.  It  bore  the  label  Popp, 
cjeschm.  Porphyr ,  Grillenburg ;  but  the  maker  of  the  section  was 
unable  to  afford  me  any  information  concerning  the  origin  of  the 
specimen  or  the  authority  on  which  it  had  been  described  as  a 
doubly-melted  porphyry/  The  microscopic  examination  of  the 
specimen,  however,  seemed  to  indicate  that  it  had  been  correctly 
labelled,  and  that  it  was  indeed  a  rock  of  very  considerable  interest. 
While  parts  of  the  section  show  the  characters  belonging  to  the 
well-known  ‘  quartz-porphyry  ’  of  Specthausen  and  Tharandt,  there 
are  other  portions  which  pass  into  a  perfect  glass.  In  this  glassy 
part  there  are  traces  of  flow-structure,  with  incipient  spherulites 
and  perlitic  cracks.  Every  gradation,  indeed,  can  be  traced  from 
nearly  unaltered  4  porphyry  ’  to  a  perfectly  vitrified  material,  and 
from  a  clear  glass  to  one  in  which  all  the  earlier  stages  of  devitri¬ 
fication  can  be  unmistakably  recognized. 
For  a  long  time  I  was  quite  foiled  in  my  endeavours  to  obtain 
any  trustworthy  information  concerning  this  remarkable  specimen 
of  the  source  from  whence  it  was  derived,  or  the  authority  on  which 
it  was  labelled.  Some  time  ago,  however,  Prof.  Zirkel  and  Prof. 
Credner  kindly  interested  themselves  in  the  matter,  and  as  a 
consequence  of  the  communications  which  they  have  made  to  me  I 
have  been  enabled  to  clear  up  my  doubts  on  the  subject.  The 
specimen  must  evidently  have  been  obtained,  not  fiom  the  locality 
named,  but  from  Ascherhiibel,  which  lies  about  3  kilometres  north 
of  a  village  now  known  officially  as  Griillenburg,  but  which  was 
formerlv  called  Grillenburg.  This  locality  is  in  the  kingdom  of 
Saxony,  and  is  nearly  equidistant,  from  Freiberg  and  Tharandt. 
At  Ascherhiibel,  the  well-known  quarz-porphyr  and  the  quarz- 
armer-porphyr  of  the  Tharandt  AN  aid  are  partial!}  covered  b} 
Quadersandstein,  the  whole  being  penetrated  by  basaltic  outbursts 
which  form  the  cupola  ( quelllcuppe )  of  Ascherhiibel,  and  the  lava- 
current  of  Landberg.  In  the  midst  of  the  Ascherhiibel  basalt  there 
are  found  numerous  inclusions  of  ‘porphyry/  in  all  stages  of  vitrifi¬ 
cation  and  fusion  up  to  a  perfect  glass,  and  it  is  one  of  these  which 
has  yielded  the  interesting  section  to  which  I  have  referred. 
Subsequently  to  receiving  this  information  from  Prof.  Zirkel,  I  was 
favoured  by  the  same  friendly  correspondent  with  an  advance  cop} 
of  the  ‘  Erkiuterungen  zur  geologischen  Specialkarte  des  Konigreichs 
Sachsen — Section  Tharandt,  Platt  81/  In  this  work  Herr  A.  Sauer 
has  given  a  short  but  very  interesting  account  of  the  eruptive  mass 
of  Ascherhiibel  and  its  inclusions,  from  which  the  following  par¬ 
ticulars  are  derived. 
Ascherhiibel  is  a  small  quellkuppe  of  an  elliptical  form,  with  a 
diameter  of  from  200  to  300  metres.  The  rock  of  which  it  is 
composed  is  a  nepheline-basalt,  and  consists  of  a  groundmass  almost 
wholly  made  up  of  microlites  of  augite  and  grains  of  magnetite, 
between  which  a  few  particles  of  nepheline  can  be  be  detected. 
