upon

[wowenglish1]

I would like to know the difference between "in which" and "upon which"


A man wished to purchase an Ass. He took the Ass home and put him in the straw-yard with his other Asses, in which/upon which the new animal left all the others.

[Anglika]

In the context of the narrative - in which = in the yard; upon which = as a result of being put with the others.