ESKER (O. Irish _eiscir_), a local name for long mounds of glacial gravel frequently met with in Ireland. Eskers (the Swedish _asar_) are among the occasionally puzzling relics of the British glacial period. They wind from side to side across glaciated country and have evidently been formed by channels upon or under the ice. "Where streams of considerable size form tunnels under or in the ice these may become more or less filled with wash, and when the ice melts the aggraded channels appear as long ridges of gravel and sand known as _eskers_. It has been thought that similar ridges are sometimes formed in valleys cut in the ice from top to bottom, and even that they rise from gravel and sand lodged in super-glacial channels. The latter at least is probably rare, as the surface streams have usually high gradients, swift currents and smooth bottoms, and hence give little opportunity for lodgment. In the case of ice-sheets, too, in which eskers are chiefly developed, there is usually no surface material except at the immediate edge, where the ice is thin and its layers upturned" (T.C. Chamberlin and R.D. Salisbury, _Geology, Processes and their Results_). Eskers are to be distinguished from kames (q.v.). ESKILSTUNA, a town of Sweden in the district (_lan_) of Sodermanland, on the Hjelmar river, which unites lakes Hjelmar and Malar, 65 m. W. of Stockholm by rail. Pop. (1900) 13,663. The place is mentioned in the 13th century, and is said to derive its name from Eskil, an English missionary who suffered martyrdom on the spot. It rose into importance in the reign of Charles X., who bestowed on it considerable privileges, and gave the first impulse to its manufacturing activity. It is the chief seat in Sweden of the iron and steel industries, its cutlery being especially noted, while damascened work is a specialty. There is a technical school for the metal industries. There are, in the town or its neighbourhood, great engineering, gun-making, and rolling and polishing works and breweries. The largest mechanical works are those of Munktell and Tunafors. The Karl Gustaf Stads rifle factory was established in 1814.