A coarse chalk gravel would probably do better in the trench than chalk dust, (the stone would not wallow, or if so, not as badly)

A few wooden boards at the head of the stone, set at an angle so as to deflect chalk beneath, (like either end of a barge), would also help

Any application of the wheel tends toward the blue end of the spectrum-of-workable-answers, (and as well those unworkable) ; perhaps too far so for them to have seen ... But i feel we should be careful not in the absolute sense : To think them inside a box, while they would have had reason to think outside one