Indeed, the presence of numerous mantle 'hot spots' over which the crust has slowly drifted to produce a chain of volcanos over many millions of years - the best known being the Hawaiian Island/Emperor Seamount Chain in the Pacific - prove without question that no crustal displacement has occurred in modern geologoical times. If it had, there would have been a noticeable break in the chain.
Rand Flem-Ath has since refined his theory to account for this by theorising a Mantle and Crust displacement (so the hot spot producing the volcano moves with the crust).
However, the really big problem with all of this is that contrary to what some writers of popular 'alternative history' have said, Anatrctica has been ice bound for hundreds of thousands of years and, during the last Glacial, had more extensive ice sheets than it does today.
A Glacial History of Antarctica
I confess that many years ago when I first came across the theory, I found it intriguing and even persuasive - until I looked into it further and realised that it's whole foundation is the misinterpretation of some medieval maps and that the proponents of the theory haven't looked properly into the geological and climatological implications of it (for example, for ECD to explain the last 'Ice Age' - which actually saw a sucession of glacial advances and retreats leading up to the most extensive glaciation c25,000 years ago - there would have had to have been dozens of displacements shifting the crust back abnd forth every few thousand years
)