In 1987, back when alt-rock was called “college rock,” the Pixies loomed large, like a bizarre crossbreeding of pop sensibilities, art-rock conceptualism and nasty guitar riffs. The elements of their sound — songwriter Black Francis’ shrieking vocals, bassist Kim Deal’s predatory bass lines, guitarist Joey Santiago’s piercing leads and drummer David Lovering’s unforgiving beats — were discernible, but they added up to something unprecedented and inexplicable, so fierce, and so weird. Their influence was far-reaching and disparate: Fans have included everyone from Kurt Cobain, who considered himself a Pixies rip-off artist, to Papa Roach, who cover the band’s “Gouge Away” on their latest album. The Pixies’ first record, an EP called Come On Pilgrim, comprised songs from an early Boston recording session. Pixies collects all the other songs taped in that session, most of which were later rerecorded and appeared on Pixies albums or singles. Even today, against a backdrop of rap rock and new metal, the frenzied riffs on “Broken Face” sound like really pissed-off birds; the previously unreleased “Rock A My Soul” screams, lurches and lives up to its title, and the prowling “Subbacultcha” resembles a recording of some sort of basement carnivore who just can’t wait to eat live rockboy. The nine tracks on Pixies clock in at just over eighteen minutes, so the CD comes off as a sketch of an unvarnished, restless band, coolly bashing out its world-domination plan, standing on the verge of getting it on.