Its surface was smooth, excepting for two lines of protuberances, each a few inches in height, and about a foot from each other.

These rows of little humps were on opposite sides of the dome, and from the bottom nearly to the top.

It was plain they were intended to serve as rude ladders by which the top of the mound could be gained.
The captain stepped back, held up his lantern, and gazed in every direction.

He could now see the roof of the cavern, and immediately above him he perceived what he was sure were regular joints of masonry, but on the sides of the cave he saw nothing of the sort.

For some minutes he stood and reflected, his brain in a whirl.