Soon everyone was peering at Sollins’ newly collected sample, wrangling over crystalline structure and trying to decide if they were looking at basalt or gabbro.

Appreciable portions of the pit are gabbro, basalt that cooled underground without erupting, that is over 1,700 million years old.

These are caused either by old intrusions of diabase and gabbro which have undergone modifications, or by later ones of dolerite.