It turns out that Atlantis and the Giants is the 1957 English edition of the 1954 book L’Atlantide et le règne des géants. It turns out that this book reads like a weird combination of Theosophy, Immanuel Velikovsky, Ignatius Donnelly, and the Nephilim, despite the fact that Saurat wasn’t familiar with Velikovsky. Instead, it takes its origins from the World Ice Theory of Hans Hörbiger as interpreted by H. S. Bellamy. This was the catastrophist idea of geology favored by the Nazis. Bellamy’s version specifically related the fall of Atlantis and the civilization of Tiwanaku to the destructive power of the giant chunks of ice that wandered the solar system, as well as the three moons he believes preceded our own. The World Ice Theory was the official cosmology of National Socialism because it was in opposition to the “Jewish” theory of relativity, and despite its manifest lack of factual basis it maintained a shadow existence among a subset of European intellectuals and publishers through the middle twentieth century.
Atlantis and the Giants centers on the reign of the Giants, which Saurat takes to be the older and more powerful race of humans who preceded us. They lived on the standard lost continents like Atlantis and Mu, and the previous ice-covered moon that once orbited the Earth was responsible for destroying their civilization when it crashed into the Earth. This (but of course) was remembered only in myth and legend, and preserved, as the author notes, in Genesis 6:4, the famous passage about the Nephilim, who were destroyed in the Flood. Saurat places a great deal of weight on Tiwanaku because he takes the eight-foot tall stone idols there to be life-size representations of the Giants, and he repeats the standard fringe history claims about how the large stones used to build it and nearby Puma Punku could have been moved, though he answer the question with “Giants” rather than “aliens.” Like other fringe figures, he agrees that Tiwanaku was once a coastal capital. You see, one of the ice-moons was once quite close to the Earth, and its gravity lifted the tides up to 13,000 feet, until the ice-moon fell apart and left Atlantis (Tiwanaku) stranded.
He also claims that “Atlantis” and its outposts contained such large buildings because during the last era of any given moon, the change in gravity as it spirals toward the earth allows humans and animals to grow to enormous sizes due to gravitational acceleration being only about 5 m/s instead of the current 9.8 m/s. This works in combination with what he says are powerful “cosmic rays” that once bathed the earth in life-giving radiation. (Hey, it was the Atom Age!) Oh, and during the interregnum between moons the lack of lunar gravity counterbalancing Earth gravity promotes dwarves and elves due to stronger pull from the Earth. (Yes, I know this doesn’t make a lot of sense.) But wait, there’s more! The last giants, after the crash of the Third Moon, became degenerate and cannibalistic, and scared modern humans worshiped them and sacrificed to them to stay safe from the monsters they mistook for “gods.”
All in all, Saurat’s 1954 book seems to bear the closest resemblance to the even more influential French book Morning of the Magicians from four years later. After all, the authors of Morning, Jacques Bergier and Louis Pauwels, mention Saurat by name, only a paragraph or so before discussing the World Ice Theory, so it’s clear they were familiar with his work and used it in preparing their own. If nothing else, there is a strange confluence of occult Nazism, catastrophism, and lost civilizations in both books, though the authors of Morning substituted aliens for giants. Perhaps the idea of gravity-induced cannibal giants was too implausible even for them!