# File lib/spreadsheet/olewriter.rb, line 122
   def write_big_block_depot
      total_blocks = @list_blocks * 128
      used_blocks  = @big_blocks + @list_blocks + 2
      
      marker = [-3].pack("V")
      eoc    = [-2].pack("V")
      unused = [-1].pack("V")

      num_blocks = @big_blocks - 1

      1.upto(num_blocks){|n|
         write([n].pack("V"))
      }

      write eoc
      write eoc

      1.upto(@list_blocks){ write(marker) }

      used_blocks.upto(total_blocks){ write(unused) }
      
   end