At length, however, after an interval of waiting that soon grew terribly wearisome, the sun went down, darkness fell, and they pushed off the boat and got under way. There was now a young moon of about four days old, and before she too set she afforded them light enough to make their way across the lower bay, a distance of about three and a half miles, to the island of Tierra Bomba, and to find the indentation to which Dick had directed Marshall's attention earlier in the day. It proved to be a particularly snug little cove, about half a mile long by perhaps a quarter of a mile wide, with thickly wooded hills sloping down toward it on either side at its upper extremity. Two small islets pretty effectually masked its entrance; and a dry sandbank in the middle of it occupied more than half its area, leaving a narrow channel all round it, the water in which was only just deep enough to afford unimpeded passage to the boat. It was stark calm inside the cove, they were, therefore, obliged to lower the sails, strike the masts, and use the oars to reach the head of the creek; but when they arrived there they found a steep bank so completely overhung with trees and bushes that, when once the boat had been forced in underneath the branches, she might remain there for days with little or no fear of discovery. In this exceedingly snug berth it seemed almost ridiculous to think of keeping a watch; yet, being in the enemy's territory, they decided to do so; Marshall undertaking to stand the first watch of two hours, while Dick agreed to take the second. When, at ten o'clock, Marshall aroused Dick, in order that the latter might stand his watch, the Captain whispered: "I've been thinking about a good many things while I have been sitting here these two hours agone in the stern-sheets of this boat. And, among other matters, I have thought that it might be very useful to know something more than we do about those two batteries that we took notice of while we were on the point yonder to-day. Now, I'm not a bit sleepy. I don't believe I could get to sleep if I tried--also the night is delightfully cool; and, although the moon has gone down, the stars give quite enough light for my purpose, therefore, I am going to take a little walk along the shore to that battery on the beach. It can't be very much more than two miles away; and night is the only time when it will be possible to examine the forts without running too much risk. If I do not feel too tired I'll take that fort on the top of the hill on my way back; so if I do not return until close before daybreak you need not be unduly alarmed." "Very well, sir," answered Dick. "We will keep a bright lookout. And if by any chance things should go amiss, and you should be pursued, if you will fire two pistol shots, one close after the other, I will come, with one of the men, to meet you, provided, of course, that we are within hearing of the shots."