“We sure will!” cried Blake.

“Isn’t it all wonderful!” exclaimed Joe, who was deeply impressed by all he saw.

“It is, indeed!” agreed the Spaniard.  “Your nation is a powerful and great one.  It is a tremendous achievement.”

Aboard the tug they went around toward the great dam that is really the key to the Panama Canal.  For without this dam there would be no Gatun Lake, which holds back the waters of the Chagres River, making a big lake eighty-five feet above the level of the ocean.  It is this lake that makes possible the operation of a lock canal.  Otherwise there would have to be a sea-level one, and probably you boys remember what a discussion there was, in Congress and elsewhere, about the advantages and disadvantages of a sea-level route across the Isthmus.

But the lock canal was decided on, and, had it not been, it is probable that the Canal would be in process of making for many years yet to come, instead of being finished now.

“Whew!” whistled Joe, as they came in sight of the dam.  “That sure is going some!”

“That’s what it is!” cried Captain Watson, proudly, for he had had a small part in the work.  “It’s a mile and a half long, half a mile thick at the base, three hundred feet through at the waterline, and on top a third of that.”

“How high is it?” asked Joe, who always liked to know just how big or how little an object was.  He had a great head for figures.

“It’s one hundred and five feet high,” the captain informed him, “and it contains enough concrete so that if it were loaded into two-horse wagons it would make a procession over three times around the earth.”

“Catch me!  I’m going to faint!” cried Blake, staggered at the immensity of the figure.

“That dam is indeed the key to the whole lock,” murmured Mr. Alcando, as he looked at the wonderful piece of engineering.  “If it were to break—­the Canal would be ruined.”

“Yes, ruined, or at least destroyed for many years,” said Captain Watson solemnly.  “But it is impossible for the dam to break of itself.  No waters that could come into the lake could tear it away, for every provision has been made for floods.  They would be harmless.”

“What about an earthquake?” asked Joe.  “I’ve read that the engineers feared them.”

“They don’t now,” said the captain.  “There was some talk, at first, of an earthquake, or a volcanic eruption, destroying the dam, but Panama has not been visited by a destructive earthquake in so long that the danger need not be considered.  And there are no volcanoes near enough to do any harm.  It is true, there might be a slight earthquake shock, but the dam would stand that.  The only thing that might endanger it would be a blast of dynamite.”

“Dynamite!” quickly exclaimed Mr. Alcando.  “And who would dare to explode dynamite at the dam?”

“I don’t know who would do it, but some of the enemies of the United States might.  Or someone who fancied the Canal had damaged him,” the captain went on.