E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Chalk and Cheese.
I know the difference between chalk and cheese. Between what is worthless and what is valuable, between a counterfeit and a real article. Of course, the resemblance of chalk to cheese has something to do with the saying, and the alliteration helps to popularise it.
This Scotch scarecrow was no more to be compared to him than chalk was to cheeseSir W. Scott: Woodstock, xxiv.
I cannot make chalk of one and cheese of the other. I must treat both alike; I must show no favouritism.
They are no more like than chalk is like cheese. There may be a slight apparent resemblance, but there is no real likeness.