Why are train tracks over log of wood?

As train tracks have to bear a weight of around 1600 tons on an average, they have to rest on objects that can stay firm as well as absorb the huge amount of energy transferred. Very strong materials like concrete can stay put, but can crack under very high force. On the other hand, wood logs have the ability to bend themselves and absorb the above energy.Then this excess energy is transferred to the ground.That is why a flexible yet strong material like wood has to be used. Too, it's cheap!.......