Yol.  49.]  GRANITE  IN  THE  GABBRO  OF  THE  CTJILLIN  HILLS.  197 
Royal  Society  of  Edinburgh  (which  the  Author  refers  to),  Sir 
Archibald  Geikie  pointed  out  that  from  the  same  neighbourhood 
where  the  4  inclusions  ’  are  said  to  occur  he  had  cited  a  remarkable 
portion  of  the  junction-line  between  the  granite  and  gabbro,  and  had 
described  the  occurrence  of  numerous  veins  proceeding  from  the  mass 
of  granite  there  and  traversing  the  gabbro.  Why  had  Prof.  Judd 
kept  silence  as  to  these  observations  ?  If  they  were  true,  they 
afforded  a  complete  demonstration  that  he  had  reversed  the  order  of 
appearance  of  the  two  rocks.  Until  they  were  disproved  it  was  idle 
to  bring  forward  such  weak  evidence  and  inconclusive  reasoning  as 
had  been  offered  in  the  present  paper.  But  the  case  against  the 
Author  rested,  not  on  the  testimony  of  this  one  locality  only,  but  on 
that  of  many  others  throughout  the  Western  Isles.  The  speaker 
referred  to  numerous  examples  described  in  his  memoir,  where,  by 
similar  proofs  of  intrusion,  he  had  demonstrated  the  posteriority  of 
the  granitic  masses.  The  granitic  veins  and  dykes  of  Skye,  Mull, 
Rum,  etc.,  not  only  traverse  the  plateau-rocks  which  Prof.  Judd 
originally  called  felstones  and  now  terms  propylites,  but  also  the 
great  cores  and  sills  of  gabbro.  The  great  granitic  bosses  are  cut 
only  by  the  youngest  basic  dykes.  Whether  these  dykes  were 
accompanied  by  the  intrusion  of  sills  or  bosses  of  basic  material  had 
not  yet  been  ascertained. 
No  man  could  pretend  to  have  exhausted  a  subject  or  a  region, 
and  Sir  Archibald  Geikie  said  he  well  knew  that  an  observer  coming 
after  him,  with  more  time  and  maps  on  a  larger  scale  than  he  had 
been  able  to  obtain,  would  correct  mistakes  into  which  he  himself 
had  fallen,  and  would  supply  a  multiplicity  of  detail  which  he  had 
missed.  He  could  only  claim  to  have  sketched  an  outline  of  a  great 
subject ;  but  he  felt  well  assured  that  when  this  outline  was  even¬ 
tually  filled  in,  the  position  which  he  had  assigned  to  the  granitic 
bosses  of  the  Inner  Hebrides  would  be  amply  confirmed. 
Dr.  Du  Riche  Preller  said  that  a  striking  analogy  existed  be¬ 
tween  the  Tertiary  gabbros  and  granites  of  Mull  and  those  of  Elba, 
with  which  latter  he  was  acquainted.  In  Elba,  however,  the  granite 
was  clearly  injected  both  into  gabbro  and  diabase,  and  was  there¬ 
fore  of  a  more  recent  Tertiary  period  than  either  of  these  rocks. 
These  rocks  occurred  in  the  schists  and  associated  calcareous  strata 
which  Signor  Lotti  had  shown  to  be  Eocene.  If  the  igneous  4  green¬ 
stone  ’  rock  of  St.  Kilda  to  which  Sir  Archibald  Geikie  referred,  and 
of  which  he  exhibited  a  specimen  showing  a  distinct  intrusive  granitic 
vein,  was  a  true  gabbro,  the  case  of  Elba  undoubtedly  tended  by 
analogy  to  strikingly  confirm  Sir  Archibald’s  view  of  the  Skye  rocks  ; 
but  the  question  was  whether  Sir  Archibald  and  Prof.  Judd  really 
referred  to  the  same  rocks.  Dr.  Preller  showed,  by  several  sections, 
the  intrusion  of  the  Elban  Tertiary  granite  into  diabase  and  gabbro, 
and  also  of  diabase  into  gabbro  :  both  these  last-named  rocks  being  in 
many  cases  altered  into  serpentine,  which  always  underlies  either 
one  or  the  other,  or  both  where  all  three  occur  together.  Some 
geologists  still  held  that  the  eruption  of  diabase  was  confined  to  the 
Palaeozoic  period,  but  the  case  of  Elba  demonstrated  that  there  the 
