Which preposition to use with crucis

as Occurrences 1%

They are admitted to surpass our American Indians, as well as the Kaffirs and the Joloffs, probably the finest African races; and a careful comparison between New-Zealanders and Anglo-Saxons will, therefore, approach as near to an experimentum crucis as any single set of observations can.

in Occurrences 1%

He could do no less; while he again and again saw hermits around him dwelling and worshipping in caves, as they had done ages before in Egypt and Syria; while he fixed, again and again, the site of his convent and his minster in some secluded valley guarded by cliffs and rocks, like Vale Crucis in North Wales.

Which preposition to use with  crucis