"We'll just hop along first to Gorgona," said Phineas. "And on the way we'll take a look at the valley of the Chagres River. You've got to understand that right here at Gatun, where we're building the dam, and where the river escapes between the hills which block this end of the valley, we shall have the end of the lake we're going to form. For the most part the valley is nice and broad, running pretty nigh north and south. This track we're on will be covered with water, so that gangs of men are already at work fixing the track elsewhere on higher ground. But I want to speak of this valley. It runs clear south to Obispo, where there is hilly ground dividing it from the valley of the Rio Grande, and there, at Culebra, which is on the hill, we're up against one of the biggest jobs of this undertaking. You see, it's like this: from Gatun to Obispo we follow a route running almost due south, with the Chagres River alongside us all the way; but at Obispo, which I ought to have said is just twenty-six miles from the head of Limon Bay, the Chagres River changes its course very abruptly, and if followed towards its source is found to be confined within a narrow valley through which it runs with greater speed, and in a north-easterly direction. Now, see here, to figure this matter out correctly let's stand up in this car. There's the track running way ahead of us through the Chagres valley in a direction I described as southerly, though to be correct it is south-westerly. Dead behind us is Limon Bay; right ahead is Panama. I've given you an idea of the works we're carrying out at this end--first dredging Limon Bay for 4-1/2 miles, then canal cutting for say another 4 miles. There you get three tiers of double locks, and the Gatun dam that's going to fill in the end of this valley, and give us a lake which will spread over an area of no fewer than 164 square miles, and which will fill the valley right away up to Obispo, where the Chagres River, coming from a higher elevation, will pour into it." "And then," demanded Jim, beginning, now that he was actually in the valley, to obtain a better conception of the plan of this huge American undertaking. "I can see how you will bring your ships to the Gatun locks, and how you will float them into the lake. I take it that there will be water enough for them to steam up to Obispo. After that, you still have to reach Panama." "Gee! I should say we had. But listen here. Taking this line, with Panama dead south-west of us, we come at Obispo to a point where the designers of the canal had two alternatives. The first was to cut up north-west, still following the Chagres valley where it has become very narrow, and so round by a devious route to Panama. That meant sharp bends in the canal, which ain't good when you've got big ships to deal with, and besides a probable increase in the cost and in the time required to complete the undertaking." "And the second?" demanded Jim.