Ramer is a Tolkien alter ego in the unfinished novel from The Notion Club Papers.
Evidence that the above boulder is the origin of Ramer's "dream-meteor" - by communion with which, the fictional character was able to travel vast distances in time and across space - is presented over at my Inklings blog.
The 'lucid dreams' associated with the meteor and described by Ramer include such experiences as Elemental Fire, endless Length of Time, and Weight" (in his notes, Christopher confirms that his father once described a dream experience of "pure Weight").
All of which suggests that the young Tolkien may have had some analogous experience with the Cannon Hill Park boulder.
To speculate: Might such a 'cosmic vision' during his early life have been an ingredient in Tolkien's later creation myth from Lost Tales and The Silmarillion: The Music of the Ainur?