According to Wikipedia:
The library was established with a bequest from Stephen Mitchell, a wealthy tobacco manufacturer, whose company, Stephen Mitchell & Son, would become one of the constituent members of the Imperial Tobacco Company. It contains the largest public reference library in Europe, with 1,213,000 volumes. While composed mainly of reference material it also has a substantial lending facility which began in 2005. The original North Street building with its distinctive copper dome surmounted a bronze statue by Thomas Clapperton, entitled Literature, often referred to as Minerva, the Roman goddess of wisdom, opened in 1911. The architectural competition for the library's design took place in 1906 and was won by William. B. Whitie. The Edwardian Baroque building is protected as a category B listed building.
The vast majority of the library's collection however is housed in the Extension Building, which was built between 1972 and 1980. Located to the west of the original building. It was originally known as the St Andrew's Halls, which were designed by James Sellars and opened in 1877. It was Glasgow's pre-eminent venue for concerts and meetings at the time. It had a massive and striking classical facade and included a Grand Hall which could hold 4,500 people, and a large ballroom. The building was however gutted by fire in 1962, although the facade survived and was later incorporated into the extension of the Mitchell Library.