A brief summary on the geology and the iron ore deposits of the Devonian Lahn Geosyncline (West Germany) is followed by the examination of the iron variation in the eruptive rocks in this area and in analogous magmatic associations elsewhere. A major strong point is the sporadic appearance of xenolithic inclusions of hematite in some keratophyres of the Lahn area. As a result, analytical, mineralogical and textural evidence is against dependence of the iron in the ore deposits on the contemporaneous femic rocks, whereas, in the keratophyre, another source of that iron is indicated. Thus two periods of magmatic events are derived. Special attention is called to the effects and conditions in the earlier period, and it may be suggested that three magmatic units corresponding to keratophyre, weilburgite and iron ore, owe their origin to the specific hydromagmatic conditions of a spilitic differentiation process in that early period.