what happened.

The train was going down grade now, and the speed was much increased.
Telegraph poles whizzed past at a rapid rate and the wheels sung a
livelier tune as they clipped over the rail joints.

"It's a good thing the engineer is going to slow down for us," said
Jack. "We'd never be able to jump off at the rate we're going."

"Hark!" exclaimed Mark. "There goes the whistle!"

The boys listened. A long, shrill blast cut the summer air, and
vibrated back to them over the tops of the cars.

"That isn't five whistles; it's one!" cried Jack. "It's the call for
brakes! I wonder if anything has happened to the train!"

There was a pause. Then came another single shriek from the engine's
whistle. It sounded appealingly, as if the steam monster was in
distress.

"Look! Look!" shouted Mark. "We are going much faster than we were!"

At the same instant there was a crash and a jolting sound. The train
seemed to break in two parts at about the centre. The forward section,
drawn by the engine, went one way, and the other part, with the gondola
containing the boys, in the lead, took another track. An insecurely
fastened switch was responsible for the accident. The locomotive and
nearly half the cars of the train took the main track, while the
remainder of the outfit swung on to a siding.