Using your knowledge of the cross-cutting nature of contact metamorphism, how could you tell whether the basalt was a lava flow or a sill?

You can tell through the nature of crystal characteristics of lava flows and sill and the cooling nature of both.

Explanation:

Lava flows cool more rapidly and are crystal in nature. Sills are formed when there is a slow cooling between the rock layers and becomes intrusive.

Basalt could be lava flow or sill when these aforementioned characteristics are noticed. Furthermore, sill can be horizontal or gentle intrusive sheet in between rock formations.

brave new world, aldous huxley (1932)