In this paper we reanalyse the set of ten major geomagnetic storms which occurred between August 1978 and December 1979. We relate them to the characteristics of the solar wind disturbances which caused them and the solar sources of such disturbances as tracked by means of interplanetary scintillation. It seems to us that the shock causing the sudden commencement and the plasma behind it with an important long-lasting B(z) south component (B(z)*) are not necessarily parts of the same structure. We also found that the solar sources of all these disturbances were regions near central meridian containing both a coronal hole and a flare or, most frequently, an erupting prominence. A possible scenario for the occurrence of these processes at the Sun is outlined, and theoretical and observational support for it is provided.