But it was different out upon the rose-tinted waters of the central lake. It boiled and heaved with strange life. Great slate-colored backs and high serrated dorsal fins shot up with a fringe of silver, and then rolled down into the depths again. The sand-banks far out were spotted with uncouth crawling forms, huge turtles, strange saurians, and one great flat creature like a writhing, palpitating mat of black greasy leather, which flopped its way slowly to the lake.