Other instruments such as the guitar, mandolin, and autoharp became popular in Appalachia in the late 19th century as a result of mail order catalogs. These instruments were added to the banjo-and-fiddle outfits to form early string bands. The fretted dulcimer— often called the "Appalachian" or "mountain" dulcimer due to its popularity in the region— emerged in Southwest Pennsylvania and Northwest Virginia in the 19th century. It is thought to have been a modification of a German instrument. Unrelated to the hammered dulcimer, the fretted dulcimer is essentially a modified zither. In the early 20th century, settlement schools in Kentucky taught the fretted dulcimer to students, helping spread its popularity in the region. Singer Jean Ritchie was largely responsible for popularizing the instrument among folk music enthusiasts in the 1950s.