I have the Concise Scots Dictionary (Aberdeen University Press, 1985, Ed. Mairi Robinson), which I find excellent.
To simplify its entry, it says that Spirk and Spark (or Sperk) are the same, and it gives three basic meanings for the word as a noun:
1. A spark (as in "Man is born to trouble as the sparks fly upwards")
2. A very small amount of something liquid or semi-liquid, a drop. And it gives three specific sub-meanings
a. A nip of spirits
b. A drop of water, a raindrop
c. A splash of mud
3. A small diamond/ruby, etc.
If RK had one of those meanings in mind, I suppose the one which I would suggest is 2c, a splash of mud. Tomlinson, in the devil's eyes, is neither a spirit nor human clay. But that's the best I can suggest.
And as a total irrelevance, there's also a nautical word 'spirketing', much used by Patrick O'Brian, which is defined as "On the side of a ship of war, the range of planks that lies between the waterways, the planking that connects each deck to the side and forms a gutter for drainage, and the lower edge of the gunports." I put that in specially for John Radcliffe!
Yours,
Alastair Wilson
