This spot they were now rapidly approaching. It consisted of a nearly straight defile, about half a mile in length, with a bend in its middle just sufficient to shut out the view of one end of it from the other. This defile was simply a cleft in the stupendous mass of rock that formed a great spur of the mountain on the left-hand side of the path, and was undoubtedly the result of some terrific natural convulsion of prehistoric times, which had rent the living rock asunder, leaving a vertical wall on either side, the indentations in the one wall accurately corresponding to the projections on the other. At the lower extremity--that is to say, the extremity which the fugitives were now approaching--access to the defile was gained by means of a sort of portal, less than six feet wide, the space between the rock walls thence narrowing gradually to about four feet, and thus forming a kind of passage about fifty feet long; beyond which the rock walls gradually receded from each other until, at the other extremity of it, the defile was nearly a hundred feet wide. The walls were unscalable throughout the entire length of the defile, which abruptly ended in a rough and torn rock face some two hundred feet in height. This rock face could scarcely be described as unscalable, because it was so rough that, although practically vertical, the projections on it were so numerous and pronounced that an active man could climb it without much difficulty, if uninterfered with; but if the summit and flanks happened to be held by even a small force of men armed with rifles, to climb it would at once become an absolute impossibility. Outside the entrance there was a small, open, grassy space, backed by dense scrub; and Jack's plan was that Carlos, with about fifty men, should enter the defile, pass through it to its upper extremity and scale the rock face there, holding it against the Spaniards, and thus checking their further advance, while Jack, and the remainder of the negroes, with the two Maxims, should secrete themselves in the scrub and remain in hiding until the entire Spanish force had passed into the defile, when they would emerge and block the entrance with the two Maxims, thus bottling up the Spaniards and compelling them to surrender--or be annihilated.