Marlowe rises from the grave ... then sinks into it again.
It's been called literary ventriloquism - the ability to write in the 'voice' of another writer. That idea, once a jeu d'esprit, has now become big business. I guess it began with Kingsley Amis writing a James Bond novel - Colonel Sun - after Fleming's death, following his own critical examination of the Bond phenomenon, The James Bond Dossier. Subsequently, Wikipedia provides a frighteningly long list of Bond books written by other writers, culminating most recently with William Boyd's poor effort, Solo.
Recently, the Booker-Prize winning author John Banville, writing in his guise as Benjamin Black, has produced a Raymond Chandler 'continuation', The Black-Eyed Blonde, apparently a title that Chandler had earmarked in his notes for future use. This follows a couple of attempts at Chandler follow-ons from the prolific and often excellent Robert B. Parker - Poodle Springs and Perchance to Dream, neither of which met with much approval from hard-boiled fans. But then, expectations are high when it comes to Raymond Chandler.