8. During a field trip with your geology class, you visit an exposure of rock layers similar to the one sketched here. A fellow student suggests that the layer of basalt is a sill. You disagree. Why do you think the other student is incorrect

As sills dont weather but lava flows do.

Explanation:

A sill is the most common form of the extrusive rocks.The sills are a parallel beds that surround the country rocks and can be confused with the solidified lava flows as the intruded sills show as partial melting and have evidence of heating.The lava flow may show a evidence of the lower sides of the flow and in addition, these flows will form a vesicle as bubbles or gas that escapes into the air.As the sills formation takes place at a lower depths and this lava flow shows sign of weathering form the surface whereas sills don't.