The Soela Formation as an independent stratigraphic unit was distinguished recently (Mens 1979, Kala et al. 1984a). Earlier, this part of the sequence was treated either as the upper part of the Tiskre Formation (Kala 1972, Keller & Rozanov 1979b) or the lower part of the Kurzeme (now Irben) Formation (Mens & Pirrus 1972).

The type section is in the interval of 230.7 to 263.7 m of the Emmaste drill core (Fig 20-117), Hiiumaa Island. The formation occurs on the islands of the West - Estonian Archipelago and in the western part of mainland Estonia (Fig. 21). It is known only from core sections, and its lower boundary coincides with the lower boundary of the Ljuboml’ Stage (see above). The upper boundary is lithologically clear, only east of the Koluvere ‑ Rumba ‑ Pärnu line it is somewhat debatable. The formation lies transgressively on the Lower Cambrian rocks or the crystalline basement (Fig. 20-257). The thickness varies from 7.9 to 41.8 m, increasing from north to south.

The formation consists of weakly cemented light‑coloured fine‑grained feldspatic (subarkose) sandstones, containing up to 10% of coarse sand and gravel grains. In the lowermost part of the section, mainly beyond the area of distribution of the Tiskre Formation, interbeds of greenish‑grey siltstones and argillaceous rocks occur. Pebbles of greenish‑grey clayballs and cross‑bedding marked by mica flakes and glauconite grains are characteristic of the lower part of the formation.