Darwin found fossilized seashells in sedimentary rock up on a mtn.What happened during the history of the mtn.?

fossilized clams have been found atop Mt. Everest. I believe in catastrophism as opposed to the preferred uniformitarianism. The bible states that God destroyed the first earth age when Satan rebelled. The then perfect earth was made void and without form (as seen in Genesis 1:2) after some cataclysmic event or events. God did not create the earth void and w.o. form, it rather, became that way - Isaiah 45:18. Anyways, in the first earth age, their was a firmament above earth. This is where all the oceans / water were. The water stayed above the planet and protected it from any impacts. The earth was watered at night by dew. Their must have also been a magnificent prism effect.