424  DR.  C.  CALLAWAY  OX  THE  ORIGIN"  OF  THE  [Aug.  1 893, 
Prof.  Bonney  stated  that  in  Dr.  Callaway’s  leading  conclusions  as 
to  the  genesis  of  the  Malvern  rocks  he  agreed,  viz.  that  largely,  if 
not  wholly,  they  were  igneous  rocks,  gneissoid  from  pressure  ;  but 
in  some  details  he  could  not  follow  him.  He  failed  to  understand 
how,  if  magnesia  were  removed  from  a  rock,  the  alkalies,  as  indi¬ 
cated  in  Dr.  Callaway’s  analyses,  remained  constant  when  almost 
everything  else  was  changed.  He  could  not  believe  in  such  a  change 
as  the  formation  of  a  quartzite  from  a  gabbro,  referred  to  by 
Dr.  Callaway  ;  and  he  had  never  seen  anything  to  confirm  the  idea 
that  biotite  was  formed  out  of  hornblende  by  way  of  chlorite. 
How  were  you  to  add  silica  and  alkalies,  and  get  rid  of  the  water  ? 
Generally  biotite  came  direct,  either  from  the  crushing  or  from 
the  melting  of  felspar  and  hornblende  together. 
Mr.  Harrer  found  difficulty  in  understanding  some  of  the 
chemical  changes  which  the  Author  believed  the  Malvern  rocks  to 
have  experienced,  such  as  the  removal  of  alumina  while  the  alkalies 
remained  practically  undiminished.  He  asked  whether  the  field- 
evidence  would  not  allow  some  of  the  supposed  transitions  to  be 
explained  by  the  intrusion  of  one  rock  into  another. 
Mr.  Rutley  agreed  with  Dr.  Callaway,  to  some  extent,  in 
believing  that  the  schists  of  the  Malvern  Hills  had  been  formed 
from  plutonic  rocks  ;  but  he  differed  from  him  as  to  the  way 
in  which  they  had  been  formed.  He  had,  indeed,  already  ex¬ 
pressed  the  opinion  that  they  had  resulted,  in  part  at  least,  from 
the  denudation  of  an  old  land  composed  both  of  eruptive  rocks  and 
sediments.  With  regard  to  the  corroded  character  of  felspars 
in  the  proximity  of  shearing-zones,  he  pointed  out  that  the  most 
corroded  felspars  which  he  had  met  with  in  the  range  occurred  in  a 
rock  which  he  had  described  as  ‘  eukrite,’  and  in  which  there  was  no 
indication  of  shearing.  The  acceptance  of  some  of  the  Author’s 
statements  concerning  the  genetic  sequence  of  minerals  demanded 
the  exercise  of  faith.  It  appeared  that  some  of  the  minute  bands 
occurring  in  biotite-gneiss,  which  the  Author  termed  granitic,  might 
merely  be  the  result  of  mineral  segregation.  On  the  whole,  he  con¬ 
sidered  that  the  paper  dealt  with  many  interesting  questions,  and, 
although  the  conclusions  so  boldly  expressed  in  it  differed  from  his 
own,  the  perseverance  displayed  by  Dr.  Callaway  in  this,  as  in  his 
previous  communications  to  the  Society,  rendered  his  work  deserving 
of  very  careful  consideration. 
Prof.  Hull  wished  that  the  Author  had  given  some  better  evi¬ 
dence  as  regards,  at  least,  one  point  connected  with  the  meta¬ 
morphism  of  the  Malvern  minerals — namely,  the  conversion  of 
chlorite  into  biotite.  In  all  his  experience  amongst  metamorphic 
and  igneous  rocks  he  had  never  noticed  chlorite  otherwise  than  as  a 
decomposition-product ;  whereas  biotite  was  a  primary  mineral,  as 
shown  by  its  occurrence  in  modern  lavas.  He  very  much  doubted 
the  formation  of  biotite  in  the  manner  stated  by  the  Author. 
The  Author,  in  reply  to  Prof.  Bonney,  said  that  the  loss  of 
alumina  in  the  change  from  diorite  to  gneissoid  quartzite  was  accom¬ 
panied  by  a  decrease  in  the  alkalies,  though  perhaps  he  had  not 
