Question

why are stones inserted at the middle of the railway track?

Answer 1

stones inserted at the middle of the railway track because stones minimize the vibration
formed by passing of train

Answer 2

Stones keeps the railway tracks jamm it helps to reduse vibrations and trains are heavy but because of stones railway tracks cannot insert in to the earth.
It is necessary to change the stones afer some time...!
You can imagine without stones beacuse of trains heavy weight tranis track goes into the earth specially in rainy days....!