Troubled by illness throughout his life, Sederholm originally chose to study geology to allow him to work outdoors. After studying first in Helsinki (where he was a student of Fredrik Johan Wiik[3]), then in Stockholm and Heidelberg, Sederholm returned to Finland to work for the Geological Survey of Finland. In 1893 he assumed the role of director of this institution, a post he occupied until his death forty years later.
Working on local Precambrianbasement rocks, Sederholm instigated a map-making programme that, between 1899 and 1925, published many maps and descriptions of their geological history. Gneisses in the areas he studied (the so-called Baltic Shield) were often of mixed composition, with layers of granitic rock being interleaved with metamorphic rock. Sederholm termed these as migmatites, and viewed them as the product of the intrusion of igneousmagma into metamorphic rocks at depth.
