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54  PUBLIC  WORKS  OF  INDIA

The  'North-western  Himalayan  series'  from  Dehra  Doon
to  Attock  was  completed  in  the  year  1853.  Its  length  is  416
miles  and  it  comprises  33,000  square  miles  of  very  hilly  country.
It  had  been  commenced  in  1847,  but  its  progress  was  inter-
rupted by  disturbed  political  conditions.  The  '  Western  longi-
tudinal series '  extending  from  the  Sironj  base  to  Karachi,  was
commenced  in  1848,  and  the  triangulation  reached  Karachi  at
the  end  of  the  year  185S,  after  five  seasons  of  extremely  arduous
labour.  The  length  of  this  side  of  the  great  quadrilateral  is  668
miles,  covering  an  area  of  20,323  square  miles.  A  portion  of  the
survey  crosses  the  '  Thur  '  or  desert  country  north  of  Guzerat,
and  its  execution  entailed  much  skilful  arrangement  and  fore-
thought for  the  due  provision  of  supplies  and  water  to  the
working  parties,  numbering  about  200  persons.
As  soon  as  tbcse^two  great  series  were  approaching  comple-
tion it  was  necessary  to  measure  the  terminal  bases  at  Karachi
and  Attock.  A  suitable  site  for  the  latter  was  chosen  in  the
'  Chuch '  Doab,  near  Attock,  on  the  east  side  of  the  Indus.
The  valley  of  Peshawiir  had  at  first  been  proposed  as  the  most
appropriate  position  for  this  base,  but  the  idea  had  to  be
abandoned  owing  to  the  disturbed  state  of  the  valley  at  that
time,  in  consequence  of  the  frequent  incursions  of  lawless  tribes
along  the  frontier,  Attock  thus  became  the  upper  comer  of
the  North-west  quadrilateral  and  a  branch  triangulation  was
subsequently  carried  to  the  fi^ntier  at  Peshawur.
