Here there are two allusions.
Eliot's note to line 360 refers us to a passage in the book South by Sir Ernest Shackleton, an account of one of his expeditions. A description of this famed expedition is at the miscellania page for line 360.
In previous notes Eliot alludes to the account of an unseen resurrected Christ walking with two of his disciples on the road to Emmaus. See Eliot's note to line 46 and his note to Part V. The story of Christ on the road to Emmaus is told in the Gospel of Luke, Chapter 24, starting with verse 13.