Although John Philip Sousa supposedly was the first to utter the adage “when in doubt...trill,” I can certainly imagine Charles Tournemire imparting this same suggestion to his students, considering that he used the technique many times especially in his larger works.
Based on Gregorian themes of the day, this “Sortie”, or Postlude, for the feast of the Assumption includes a subtle nod to bitonality in the softer sections of the work, making this piece rather avant-garde for the organ world in 1928.
This work is the last movement of no. 35 in the complete "L'Orgue Mystique" collection. Luckily, the entire collection is available on IMSLP.
(At 1080p this video recording has an unusually large dynamic range. If the volume is set so that you can hear the tracker action on the Récit, you may have to turn it down a bit for the tutti sections.)
I love this sample set and I hope you enjoy this recording.