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Abstract
A group of small diatomite deposits occur within the outcrop of a serpentinite forming part of the Shetland Ophiolite. They occur on sloping hillsides where no standing water can have existed, often adjacent to springs, and in the beds of abandoned streams. They vary in size from a few metres in diameter and several centimetres thick to more than 100 metres across and nearly a metre thick. No diatomite has accumulated in ponds in the area at depths of less than one metre due to wind disturbance. It is suggested the diatoms lived in springs and in their outflow and that they accumulated as sieve-type deposits where the spring water seeped away into the ground and eventually through the accumulated diatomite. Two l4C dates from peat immediately underlying diatomite indicate deposition following 2380 and 1570 BP. The chemical influence of the serpentinite, then as now, inhibited the growth of plants and peat on the serpentinite, thus making possible the accumulation of diatomite instead of peat.