Vol.  49.] 
SHEET  OF  DIABASE  AT  ROBIN  HOOD. 
538 
may  be  seen  with  the  aid  of  a  pocket-lens,  shining  with  a  bright 
metallic  lustre,  but  they  are  rarely  large  enough  to  be  seen  with 
the  unaided  eye.  The  miners  who  obtained  antimony  from  Robin 
Hood  Mine  were  also  aware  of  its  presence  in  the  grit,  and  made 
several  small  excavatious  in  it  similar  to  those  in  the  diabase. 
The  following  are  analyses  of  typical  specimens  of  the  diabase 
and  grit,  the  former  taken  from  the  head  of  the  old  shaft  near  Robin 
Hood,  and  the  latter  from  one  of  the  excavations  about  one-third  of 
a  mile  north-east  of  the  shaft.  The  specimens  were  analysed  in 
the  laboratory  of  Mr.  R.  Hellon,  Ph.D.,  F.I.C.,  Public  Analyst  for 
the  counties  of  Cumberland  and  Westmoreland,  by  that  gentleman 
and  his  assistant,  Mr.  J.  E.  Brockbank,  E.C.S. 
I.  Diabase. 
Silica  . 
...  48-42 
II.  Grit. 
Silica  . 
79-92 
Alumina . 
...  24-35 
Alumina  . 
5-10' 
Ferric  Oxide  . . 
...  1-00 
Ferric  Oxide  . 
trace 
Ferrous  Oxide  . 
...  8-22 
Ferrous  Oxide . 
3-73 
Lime  . 
...  5-22 
Lime . 
•89 
Magnesia  . 
...  3-20 
Magnesia . 
■85 
Manganous  Oxide  . 
...  -09 
Manganous  Oxide  . 
3-76 
Carbon  Dioxide . . 
...  6-97 
Carbon  (in  carbonaceous  matter) 
•44 
Sulphur  'Trioxide  . 
...  1-08 
Sulphur  . 
•09 
Arsenic  . 
...  -06 
P  kosphoric  Acid . . . . 
•02 
Antimony  . . . . 
...  -02 
Antimony  . 
•06 
Lead  . 
Lead . 
•02 
Copper  . 
Potask  . 
•68 
Cobalt  . 
Soda . 
1-55 
98-63 
Water  (combined)  . .  2T5 
99-26 
The  above  analysis  was  made  on 
the  rock  freed  from  hygroscopic  water 
by  drying  at  212°  Fakr. 
I  had  a  number  of  slides  prepared  from  specimens  of  the  diabase 
and  associated  rocks.  Prof.  Bonney,  E.R.S.,  very  kindly  examined 
them  for  me,  and  he  has  given  me  permission  to  make  use  of  his 
notes  in  the  following  paragraphs. 
Slide  A  was  taken  from  a  specimen  of  the  diabase  obtained  from 
Bassenfells  Quarry,  at  the  western  end  of  the  intrusive  sheet.  The 
rock,  which  appears  to  have  had  an  ophitic  structure,  consists  of 
felspar,  much  decomposed,  probably  plagioclase,  viridite  replacing 
a  pyroxenic  mineral,  grains  and  granules  of  iron  oxide  (the  exact 
species  difficult  to  determine,  probably  in  part  hydrous),  also  some 
grains  of  a  clear  mineral  which  look  like  quartz — but  the  possibility 
of  a  secondary  felspar  must  not  be  overlooked.  There  is  a  vein  of 
calcite  showing  marked  twinning  with  rather  unusually  bright  colours. 
The  rock  may  be  grouped  with  the  diabases,  but  if  the  clear  grains 
are  quartz  the  percentage  of  silica  would  probably  be  rather  high ; 
still  diabase,  in  the  sense  of  altered  dolerite,  will  be  a  safer  name 
than  diorite. 
No.  2  was  taken  from  a  specimen  of  the  diabase  obtained  in  a 
