How did the fire start?

One Saturday morning a careless motorist threw a lighted cigarette out of his car ten miles west of the small Canadian town of Stanton. The forest at the side of the road was dry because there had been no rain for many days. Within a few minutes, the bushes and trees were on fire.
    A truck driver saw the fire when he was on his way to Stanton. As soon as he reached the town he told the police about the fire. Soon firemen were hurrying westwards. When they reached the fire they saw that it was very big. It could not spread to the north because of a lake or to the south because of a wide river. But a west wind was carrying the fire towards Stanton and the firemen could not stop it. When they realized this, one of the firemen sent a message back to the town by radio.
    The chief fire officer and hundreds of people hurried to a place about half a mile west of the town. There they used a powerful explosive to blow down the trees and clear a wide path through the forest. When the fire reached the break, it began to die down because there was nothing left to burn.