gem miningThe great majority of pits are simple shafts without any  lateral  galleries or  headings.   Where  the  bottom of the shaft is above the ground  water table, adits or tunnels  are  driven  along  the  illam layer  but  they  do not  extend  far  because of the  problem  of ventilation. At times adjoining  pits are interconnected  by  tunnels. In some of the deeper shafts where the cost of excavation  is high,   lateral  drifts are driven  in  all directions from the base of the shaft so that as much gravel as possible is collected  through a single shaft. This  is by  far  the  commonest  method  of  gemming  and  in heavily gemmed areas  the ground  is riddled  with pits and connecting tunnels. In the early years of the century, Coomaraswamy   commented   "a   gemmed  out  deniya should  be seen to  be appreciated; the place is turned into a rabbit-warren of  pits and tunnels, and  if the illam  is  good  every  pound  of it  has  been  excavated and  washed".