Nida 23a - Formation of Mountains

The gemara asks that if a woman would discharge something in the shape of a mountain, it should qualify a birth to make her tamei since the term יוצר is used in the context of mountains as it is by humans. The gemara says that it isn't considered a "mountain" if it is discharged from a woman's body, it is merely a stone or clump of dirt. However, the yerushalmi answers that the Torah doesn't use the term יצירה on the initial creation of mountains, therefore it cannot be learned from a person.

Scientists consider mountains to have formed through the earths plates colliding into one another, causing them to both rise or one to end up on top of the other. The Maharatz Chiyus cites "stories of nature" that the original creation of the earth didn't contain mountains or valleys, it was a smooth ball. However, over time given various weather conditions and the mabul (flood), mountains and valleys formed. He explains that it is for this reason that we are able to find bones of animals and remnants of plant life at altitudes above where they can survive. They were originally living at lower altitudes and later rose up with the formation of mountains. This is somewhat consistent with scientific theory. According to this Hashem didn't "create" mountains during sheishes yimei b'reishis, rather they formed later. This is what the yerushalmi may mean by it not saying יצירה by the original creation of the mountains, because there was no original creation of the mountains. They were formed afterward over time by the nature that Hashem carved into the world, indirectly, so it wouldn't be accurate to use the term יצירה or בריאה to refer to mountains during the time Hashem created the earth.
This approach seems to be refuted by the Mishna in the 9th perek of Brachos that says that on mountains we make a blessing of עושה מעשה בראשית. Clearly, chazal consider mountains to have been created during the 6 days of creation, and not formed later.