In 1899 he discovered the Cioch, a unique rock feature on the Coire Laggan face of Sron na Ciche. This he climbed in 1906 with Mackenzie, who named it from the Gaelic word for a breast. Collie was instrumental in producing much better maps of the Cuillin which had previously defied the skills of cartographers. He is commemorated in the Cuillin by Sgúrr Thormaid (Norman's Peak; pronounced Skoor Horamitch) He is also remembered in "Collie's Ledge", a famously exposed rocky scramble across the west face of Sgùrr Mhic Choinnich, (MacKenzie's Peak) which is named after his great friend. Since the first traverse of this ledge was made by MacKenzie with the Irish climber, Henry Hart, rather than Collie himself, some authoritative publications have begun to use the name "Hart's Ledge"