The War Chief (All-Story) This 1927 magazine cover looks almost exactly like the 1928 book, and both are by Paul Stahr. via
The Metal Monster Four daring Americans enter a lost valley to discover a horrifying world of living metal which plots the annihilation of mankind This entire book can be read here via, via, via and via
Dwellers in the Mirage A Lost Land, A Beautiful Witch, And A Supernatural Horror From The Ends Of Time! via via via via
The Ship of Ishtar (1945) This is the 4th cover for this story I have posted, and the least sexy. via