1. A tree, fallen across the track, delayed the train.
2. The traveler, blinded by the snow, lost his way.
3. The horses, frightened by the electric car, dashed up the street.
Action must have taken place to produce states of being fallen, blinded, or frightened.
We can also think of the fallen tree, the blinded traveler, and the frightened horses.
We not only see that action is expressed by these words, but we see also that they express past action.
They are therefore past participles.
A past participle is a participle that represents an action or state as completed.