Yol.  49.]  THE  PETEO GRAPH Y  OF  THE  ISLAND  OF  CAPRAJA. 
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9.  The  Petrography  of  the  Island  of  Capraja.  By  Hamilton 
Emmons,  Esq.  (Communicated  by  Sir  Archibald  Geikie, 
I). Sc.,  LL.I).,  For.Sec.B.S.,  E.G.S.  Bead  January  11th,  1893.) 
Contents. 
1.  Topography  of  the  Island  . 
2.  Geological  Features  of  the  Island . 
3.  Macroscopic  Characters  of  the  Rocks  _ 
4.  Microscopic  Characters  of  the  Andesites  . 
5.  Microscopic  Characters  of  the  Anamesites 
6.  Chemical  Analyses  of  the  Rocks  . 
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1.  Topography  of  the  Island. 
The  Island  of  Capraja,  situated  43°  2'  35”  lat.  H.  and  9°  50'  45” 
long.  E.  of  Greenwich,  according  to  the  Admiralty  chart,  constitutes 
one  of  the  northernmost  members  of  the  Tuscan  Archipelago.  From 
it  on  a  clear  day  the  observer  can  easily  see  the  Island  of  Elba  to 
the  south-east,  Monte  Cristo  and  Pianosa  to  the  south,  Corsica  to 
the  south-west,  and  Gorgona  to  the  north,  besides  a  long  stretch  of 
Apennines  ranging  east  and  north-east. 
The  island  is  roughly  oval ;  its  longest  axis,  lying  almost  north 
and  south,  measures,  according  to  the  Italian  Ordnance  Map,  8  kilo¬ 
metres  (5  miles)  ;  and  from  east  to  west  nearly  4  kilometres 
(2|  miles)  in  the  broadest  parts.  A  chain  of  hills,  ranging  in 
height  from  350  to  450  metres  (1150  to  1475  feet),  traverses  its 
entire  length ;  the  eastern  slopes  of  these  hills  fall  away  gradually, 
while  the  western  plunge  abruptly  to  the  sea,  often  in  precipitous 
cliffs,  or  deep  ravines,  exposing  the  structure  of  the  island  re¬ 
markably  well.  The  east  coast  also  is  bounded  by  a  line  of  cliffs  : 
and  these,  though  generally  much  lower  than  the  western  cliffs, 
offer  equal  facilities  for  study.  Only  at  one  point  on  this  side  of 
the  island  do  they  reach  a  height  comparable  with  the  cliffs  on  the 
west,  i.  e.  beneath  the  twin  hills  of  Monte  Campanile  and  Monte 
Majone. 
Inland,  the  slopes  are  everywhere  cut  into  by  little  valleys,  which 
present  a  chequered  colouring  of  green  and  grey,  due  to  the 
weathered  boulders  of  andesite  standing  out  above  the  stunted, 
broom-like  vegetation.1 
In  general  terms  the  island  may  be  said  to  consist  of  a  number  of 
andesitic  outflows,  resting  on  andesitic  breccias  and  agglomerates. 
The  latter  doubtless  owe  their  origin  to  the  eruption  from  which  the 
main  mass  of  andesite  subsequently  sprang. 
1  Except  for  a  few  garden -patches  around  the  town  of  Capraja,  and  a  few 
vineyards  in  the  Penal  Settlement  at  the  northern  end,  the  island  is  devoid  of 
cultivation. 
G.  J.  G.  S.  Ho.  194.  k 
