Which preposition to use with astound

at Occurrences 10%

The two companies replied to the shot by a general volley, and rushed to the assault of the barricade, leaving behind them the seven Representatives astounded at being still alive.

by Occurrences 2%

Astounded by, this bewildering confession, and fearful that the uncle of Mr. DROOD would be back in his chair and asleep again if he gave him a chance, the excited inquisitor sprang from his chair, and slowly and carefully backed the wildly glaring object of his solicitation until his shoulders and elbows were safely braced against the mantel-piece.

Which preposition to use with  astound