My verdict: The kaldanes and the rykors of The Chessmen of Mars didn't bother me; but I found the indiscriminate brain-swapping in this novel rather revolting. I could've forgiven this, though, if Burroughs had found some clever way to have the protagonist, Ulysses Paxton (a.k.a. Vad Varo), defeat the mad scientist using brain-swapping. But really it just functions as a MacGuffin for the love/adventure story and for Burroughs to reiterate that his opinion that being too smart is a bad thing. Unfortunately Burroughs had nothing to add to the theme that he hadn't already expounded in The Chessmen of Mars. He also takes another stab at organized religion, though this time it has the advantage of being amusing, not just simplistic.
 Read my review here.
 I'd say it's nice to finally get away from the Carter family, but Vad Varo (a.k.a. Ulysses Paxton) is the same character, just with a different backstory and a different name. He had far too easy of a time winning people to his cause, even though they all warned him that it was impossible.
 For his previous attempt, see my review of The Gods of Mars, here.
Volcanic Rocks on Mars is by Mars Exploration Rover Spirit (NASA) and exists in the public domain. It is available at http://www.nasa.gov/multimedia/imagegallery/image feature 645.html.