Sentence:  I was now able to observe that the sailors, marooned on the benches, tables, and other islands of refuge, were roughly <WSD>dividable</WSD> into three classes—the prostrate ones, who heaved drunkenly to the roll and took no notice of the primal chaos about them; the semi-prostrate ones, who were still able to exhibit mild resentment when the tidal wave engulfed or threatened to engulf them; and the others—some lounging easily, but the most perched or roosted on some dry but precarious pinnacle—who quaffed great mugs of hot tea and bit hungrily into hunks of bread and smoked fish. 
Meaning of the word marked with <WSD> tags:  Capable of being divided ("into" fractions or parts).