Hollow Earth

A wonderful article.
Walking Upon Hollow Earth: The Juvenilia of H.P. Lovecraft
by Abbey Kerins
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Link:
http://dl.lib.brown.edu/pdfs/1172071142468750.pdf
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Compare the Argosy series of fictional articles by Park Wintrop.
"The Land of the Central Sun" (July 1902 to January 1903 Argosy )
One suspects HPL would not likely have missed this. It was on Antarctica, a personal favorite topic.

Recall his letter to the editor in Providence Journal Sunday Edition on August 12, 1906 — denouncing the popular hollow earth theory as “figments of imagination”
and an “untenable” hypothesis.