Dr. Franz Joseph Unger (1800-1870) was an Austrian botanist and palaeontologist. He ventured outside his natural ‘comfort zone’ when he wrote Die versunkene insel Atlantis (The Sunken Island of Atlantis). In it he supported the concept of Atlantis as a landmass in the Atlantic,* in an attempt to explain the similarity of flora on both sides of the ocean.*
This was the prevailing theory at the time, which was more fully expounded a couple of decades later by Ignatius Donnelly. Unger’s contribution is now available as a free ebook(a) .
(a) https://books.google.de/books?id=jRVUtihwkhEC&pg=PA1 (German)