But it was too late.

In her effort to outstrip him, Julia slid heavily into the danger zone.
There was a crash and a splash, then down she went into the icy water, followed by Tom, who had seized her arm in a fruitless effort to save her.
For an instant Tom was paralyzed with the coldness of the water.

Still, keeping a firm grip on the arm of the girl who had been responsible for his ice bath, he managed to clutch the ledge of ice made by their fall with his free hand.
"Take hold of the ice and try to help yourself a little," commanded Tom.
Julia made a half-hearted attempt, and managed to grasp the ledge, but her hold was so feeble that Tom dared not withdraw his support He was powerless to act, and they would both drown unless help came quickly..