AbstractSystematic observations on Mikkaglaciären in northern Sweden are presented and a general discussion is given concerning drainage connected with structures in the upper layer of a glacier. The basic conditions (surface drainage and structural pattern) for this drainage are first analyzed. A series of observations on“drainage structures”during a five-year period is presented and reproduced on a map (Fig. 7). Descriptions and comments are given as to the formation and further development of observed glacier mills and related features, with regard to local environmental characteristics and to the time factor involved. The development is studied also in its correlation to the transfer and rotation of the initial, mill-localizing cracks, and as regards the mutual relationships between neighbouring mill units. Different possibilities of recognizing sub-surface inter-connections between mills are commented on, and an obliquely transverse deflection of the upper parts of sub-surface drainage courses is pointed out. This drainage characteristic leads to a consideration of the most probable, near-lateral location of the further reaches of internal drainage courses.