558  PROF.  J.  W.  JUDD  ON  COMPOSITE  DYKES  IN  ARRAN.  [XoV.  1893, 
the  connexion  of  these  dykes  south  of  the  King’s  Cave  with  the 
plexus  of  Tormore  is  more  problematical,  I  have  not  included  them 
in  my  account  of  the  district. 
Fig.  5. — Diagrammatic  Plan  of  Southern  Composite  Dyke,  Tormore. 
[Total  width =90  feet.] 
s=Sandstone.  i^Quaitz-felsite  (ELyolite  and  Quartz- 
<z= Augite-andesite.  pantellerite). 
IX,  Chemical  Composition  of  the  Tormore  Dykes. 
Although  we  possess  no  published  analyses  of  the  augite- an  desites 
of  Tormore,  there  can  he  no  doubt  that  their  composition  is  fairly 
represented  by  Analysis  I.  in  this  paper  (p.  545),  and  by  the 
analyses  of  the  Xorth-of-England  Dykes  published  by  Mr.  Teall. 
The  4  vitropliyric  ’  augite-enstatite-andesite  has  been  analysed  by 
Mr.  Magnus  M.  Tait,  F.C.S.,  and  his  results  are  given  under  IV. 
below ;  it  is  the  least  acid  of  all  the  4  pitchstones  5  of  Arran  that 
have  yet  been  chemically  examined. 
The  more  acid  rocks  of  the  southern  composite  dyke  are  represented 
in  Analysis  Y.,  made  by  the  same  chemist,1  while  YI.  and  YIL  are 
analyses  of  still  more  acid  dykes  of  semi- vitreous  character  which 
occur  in  the  cliff  a  short  distance  south  of  the  area  described  in  these 
IV. 
Y. 
VI. 
VII. 
Silica  . 
72-50 
77-99 
73-84 
Alumina . 
....  12-55 
11-53 
11-17 
10*10 
Oxides  of  iron  . 
....  2-75 
2-06 
1-12 
1-24 
Oxide  of  manganese  . 
0-16 
Lime  . 
....  2-80 
1-79 
0-93 
1-17 
Magnesia  . . 
....  2-33 
2-72 
trace 
trace 
Soda  . 
....  502 
3-37 
4-93 
2-65 
Potash  . 
....  443 
5-24 
trace 
2-43 
Water  . 
....  4-20 
0-70 
3-59 
8-19 
99-81 
99-91 
99-89 
99-62 
1  Brvce,  ‘  Geology  of  Arran,’  4t,h  ed.  p.  203. 
