309. Impossibility.

Factors existing at the time of the contract may make its performance wholly or partly impossible1. It may prove impossible to construct the works at all or to do so by the proposed method of construction. Where it is impossible to carry out the works at all, it is a question of construction whether the parties intended that the contract should in such circumstances cease to bind them2. If the contractor has expressly or impliedly undertaken to complete the contract, he will be liable in damages in the event of his failing to do so, notwithstanding that the completion