It sounds more like-----" "Cavalry on a gallop," suggested Greg.
"Just what it does sound a lot like," Prescott nodded.

Then he dropped to the ground, holding one ear close to the earth.
"And, whatever the rumble may be," Prescott went on, "it travels along the ground.

Just get your ears down, fellows." "It's something big, and it's moving this way," cried Dave.
"It can't be cavalry," Tom argued.

"There are no manoeuvres on; there is no state camp ever held in this part of the state, either.
What do you-----" But Dick Prescott was up on his feet by this time.

Furthermore, he was running.