Casting the spell Raise Land on one of these weird cliff/land tiles that get created when raising land in the ocean also raises adjacent land, if this land contains a resource such as a Gold Mine or Old Forest.

Longer version if the above was confusing:

Living on a tiny island I decided to increase my land mass. To do this I stepped to the edge of my land as far as possible. Couldn't go all the way, as cliff tiles are not accessible. I cast my first raise land into the ocean right next to the cliff. Doing this created a theoretically accessible land tile in the ocean, however the cliff was still inaccessible - but now looked like Frankenstein's Cliff. To fix this malformed cliff (which seems to essentially be a cross between ocean and land) I also cast Raise Land targeted on it. While this fixed the cliff, and did not further affect any connecting normal land tiles - each time I cast this on a tile next to a resource, the resource tile was raised into a hill.

The hill being created on the resource tile covers up the resource by the way. It still works, but is basically invisible - and the land tile cannot be lowered again.