There is much debate in the literature about the raised beaches that are ubiquitous on the Isles of Scilly. They are almost everywhere -- it is almost impossible to take a half-day walk along the coastline of any one of the islands without seeing a raised beach exposure somewhere. The classic raised beach location -- at Watermill Cove, on St Mary's Island -- is in fact one of the least spectacular, and its importance to geomorphology lies not in the beach characteristics but in the characteristics and dating of the overlying sediments. By far the most spectacular examples of the raised beach are to be seen in the bay of Porth Killier, at the northern tip of St Agnes Island. A few photos of it are shown at the head of this post.
The cobbles in the photos above are for the most part well-rounded, and in some parts of the beach they are well packed together, and in others held in a sandy and silty matrix. The beach here is partly or solidly cemented with iron oxide and manganese oxide cement -- this is a common feature, but there are some places where the beach is uncemented, and friable enough to extract cobbles with ease from exposures. Note that in all of the examples shown above, there are rounded erratics incorporated in the beach, suggestive of the incorporation of foreign materials from earlier glacial episodes.
At Porth Killier, there are not many sediments above the raised beach, because there are no adjacent steep slopes which could supply abundant slope materials over a prolonged period of time; although in the lower photo we can see an overlying layer of rich brown blown sand (with signs of layering) and a modern organic-rich soil horizon. In some exposures at the northern end of St Agnes, thin glacial deposits lie directly on the raised beach or on the blown sand layer.
Most of the raised beach deposits are found at around extreme high-water mark, but some are found down to mid-tide mark, beneath the cobbles and boulders of the present-day beach. No raised beaches were found more than 5m above HWM -- so in all respects these raised beaches can be matched with those of Pembrokeshire.
Mitchell and Orme (1967) considered that there are TWO raised beaches on the Isles of Scilly, dating from different interglacials. They may have been influenced in this hypothesis by the fact that some beaches are cemented and stained with a black manganese oxide crust, while others are "fresh" in appearance. They also cited localities where an apparent "lower" raised beach was separated from an apparent "upper" raised beach by an intervening sandy layer. Scourse and other later researchers have disagreed with this assessment, and have argued forcefully that there is but ONE raised beach on the Isles of Scilly, dating from the Last Interglacial, which shows considerable variation in its altitude above OD and in its internal characteristics. I agree with this latter interpretation; I have seen no evidence to suggest that the raised beaches in the Scillies are of different ages.