Garrett P. Serviss (1851-1929) was an American astronomer and populariser of science and the author of a number of science fiction novels. In one of them(b), he was possibly the first to propose that the pyramids had been built by aliens, specifically, Martians.
Although he had a law degree, he never practised as an attorney, instead turning to journalism.
Serviss was clearly sympathetic to the idea of Atlantis, located in the Atlantic but never committed fully to the idea, although he was content to echo the views of those scientists of his day who did(a).
*However, in 1915, Serviss put forward the possibility that a lost continent in the Arctic Ocean, containing Atlantis, was destroyed and that this cataclysm also generated Noah’s Flood.(c)*
(b) https://archive.org/details/edisons_conquest_of_mars_0806_librivox (print + audio)