You couldn't really call him a professional geologist but that's just because he was so filthy rich he didn't have to work!
Don't forget that people of his time were polymaths, too, and that Natural History was an especially eclectic field by today's standards.
If I recall correctly, he was the first one to figure out why coral atolls have a central lagoon. He also wrote a comprehensive monograph on barnacles (I recall that he spent years dissecting many, many different specimens sent to him in an effort to catalog all the known species).
Actually, if their god makes better pancakes, I'm totally switching sides. --
Charley the Australopithecine