Answer:
Before mountain building occurred, the area was underwater.
Explanation:
Through excavation, fossils that are of marine animals are often found high on mountain ranges. This seems weird from today's perspective, as marine animals can only be found in ocean waters, and there is no way they can travel on land and upon the mountains. Earth has changed a lot throughout history though, so such occurances are actually not that weird.
The mountains in Pennsylvania are such a place, with an abundance of marine fossils. When we look at the geological past of what is now Pennsylvania we can easily see why this is the case. The whole area was actually underwater for millions of years. This was the case before mountain building occurred here when part of the ocean floor raised high above the surface of the water and created land. As the crust was going up, the fossils on it went up as well.
