With rare exception, dredge hauls recovered young glassy pillow lavas with no ferromanganese crust or sediment cover (Cousens 1982).
A 1994 cruise (PGC94-04) recovered glassy pillow lavas from a flow just south of the 1970 dredge on the northwestern knoll.
Pillow lavas form where lava is extruded under water.
The young rocks are
pillow lavas, created when molten rock comes in contact with cold water.
The
pillow lavas have often Basaltic composition and have gone under spilitisation phenomenon process, and minerals like Albite, chlorite, Calcite, Zeolite, Serpentine, etc.
Alison Lea-Wilson, Angleseybased chairman of Tourism Partnership North Wales, said the island's geology was accessible to non-experts through features such as the cliffs of South Stack and the Precambrian
pillow lavas of Llanddwyn Island.
While most of these drill holes produced "normal" sections of extrusive basalts occurring as
pillow lavas and flows, a few holes crossed peridotites or gabbros, either just beneath the sediment cover or within the lava sequence.
On three previous legs, researchers had drilled through sediments and
pillow lavas and into the sheeted-dikes layer, to a total depth of 1,350 meters below the seafloor.
In Archean rocks, scientists had previously found only sediments and
pillow lavas, leading some to suggest that these rocks were created not by seafloor spreading in deep oceans but in the shallow seas that formed over continents as they were rifted apart.