They were trying to kindle a fire-with flint and steel, under the shelter of the boat.

He continued to watch them 'lazily and without alarm.
Their fire, if they succeeded in making it, would cast no light upon him in the dense covert, but they would be outlined against the flame, and he could see them better, well enough, perhaps, to tell to what tribe they belonged.
He watched under his lowered eyelids while the warriors, gathered in a close group to make a shelter from stray puffs of wind, strove with flint and steel.

Sparks sprang up and went out, but Henry at last saw a little blaze rise and cling to life.

Then, fed with tinder and bark, it grew under the roof made by the boat until it was ruddy and strong.

The boat was tilted farther back, and the fire, continuing to grow, crackled cheerfully, while the flames leaped higher.
By a curious transfer of the senses, Henry, as he lay in the thick blackness felt the influence of the fire, also.