As it were (ως). "As if," not a great mountain, but a blazing mass as large as a mountain.

Burning with fire (πυρ καιομενον). Present middle participle of καιω. Somewhat like Enoch 18:13, but perhaps with the picture of a great volcanic eruption like that of Vesuvius in A.D. 79. Strabo tells of an eruption B.C. 196 which made a new island (Palaea Kaumene).

Became blood (εγενετο αιμα). Like the Nile in the first plague (Exodus 7:20). Cf. also Revelation 16:3.