shares of canadian national railway co cnr slipped 068 to c16124 tuesday in what proved to be an allaround negative trading session for the canadian market with the sptsx composite index gsptse falling 101 to 2040756 canadian national railway co closed c1415 short of its 52week high c17539 which the company reached on december 13th trading volume of 725712 shares remained below its 50day average volume of 13 m