Peter Buckley noted Nico's use of psychedelic drugs during the Summer of Love as an influence on the album's music, and Jim DeRogatis described it as "minimalist bad-trip psychedelia". AllMusic has categorized the album as art rock. "frieze" called "The Marble Index" the "bridge between the New York Minimalists of the late 1960s and Brian Eno's ambient records of the late 1970s". Simon Reynolds has identified the album as "the rock precedent for isolationism", a term coined by critic Kevin Martin to describe "a loose network of disenchanted refugees from rock and experimental musicians" that originated the genre known as dark ambient. Isolationism, Reynolds writes, "breaks with all of ambient's feel-good premises", and "evokes an uneasy silence: the uncanny calm before catastrophe, the deathly quiet of aftermath." He listed Aphex Twin (particularly his 1994 album "Selected Ambient Works Volume II"), Seefeel, David Toop and Max Eastley, among others, as exponents of this style.