John Glascock (2 May 1951 - 17 November 1979) was the bass guitarist, backing vocalist, and occasional lead vocalist for the progressive rock band Carmen. He was also the bass guitarist and backing vocalist for the progressive rock band Jethro Tull from December 1975 until August 1979. He died in 1979, at the age of 28, as a result of a congenital heart valve defect, which was worsened by an infection caused by an abscessed tooth. In a September 1978 'Guitar Player' interview, Ritchie Blackmore had said "...

Glascock then joined Jethro Tull in 1976, after having met Ian Anderson when Carmen opened several dates for Jethro Tull on their War Child tour. Martin Barre said in the "Classic Artists Series" documentary, that his love for the band was unique, being a fan of Jethro Tull playing in the band. He played on the Jethro Tull albums Too Old to Rock 'n' Roll: Too Young to Die! (1976), Songs from the Wood (1977), Heavy Horses (1978), Bursting Out (1978), and on three tracks on Stormwatch (1979). In Jethro Tull he received no writing credits but sang backing vocals, and became the first harmony vocalist Jethro Tull had. He even sang on the album he was not credited on, Heavy Horses (1978).  Glascock replaced the longtime friend of Ian Anderson, Jeffrey Hammond. He also played electric guitar on-stage when Anderson's arrangement required it, as for instance in performances of "Skating Away (On the Thin Ice of the New Day)" from the Bursting Out live album, when the rest of the band was playing xylophone, glockenspiel and percussion.  Glascock's health problems became apparent when he was unable to complete the U.S. leg of the Heavy Horses tour, missing a transatlantic simulcast from Madison Square Garden. He played his last gig on 1 May 1979, in San Antonio, Texas, three years to the day of his first gig with Jethro Tull. Despite the diagnosis of heart valve damage caused by an infection, he continued his previous lifestyle, which involved heavy drinking, marijuana usage, and wild parties. His health continued to deteriorate. Ian Anderson gave him several warnings before finally laying him off with pay during the production of Stormwatch (1979), completing most of the bass guitar parts himself. During the subsequent promotional tour with replacement bass player Dave Pegg, Anderson learned of Glascock's death and had to break the news to the rest of the band. Glascock's close friend, drummer Barriemore Barlow, was devastated and left the band at the end of the tour. Mark Craney replaced Barlow.  The resulting dislocation, Ian Anderson's own artistic vision, and a decision from the label, prompted a complete overhaul of the lineup, leaving only Anderson and Martin Barre as full members, though Glascock's touring replacement on bass (Dave Pegg) was retained for the band's follow-up album in 1980. Answer this question using a quote from the following article:

Did they tour?
when he was unable to complete the U.S. leg of the Heavy Horses tour,