Moist semi-oxygenated particles of iron, it is well known, have an agglutinating power; – the AGGLESTONE, therefore, which is composed of ferrugineous sand-stone, appears to me to have been formed on the spot, and there can be no necessity for supposing that the Druids (if it be true that it is a Druidical monument) would bring so enormous a mass from a distance. --
This extraordinary insulated rock, is situated on the heath, not far from Studland, and is about eighty feet in circumference, at a medium, the height being about twenty. It is somewhat in the shape of an inverted cone. The spot whereon it stands is raised like a barrow. This circumstance occasioned the conjecture that it was erected as a monument to some British chief, interred below. Whether it was intended for a sepulchral memorial, or whether the heap of earth was thrown up only to render the top of the rock accessible, the name Agglestone (from the Saxon halig-stand, i.e. holy stone) certainly seems to shew that it was erected for some superstitious purpose.
The country people call it the Devil’s night-cap, and there is a tradition that his Satanic Majesty threw it from the Isle of Wight, with an intent to demolish Corfe Castle, but that it dropped short here!
From volume 1 of “Observations relative chiefly to the natural history, picturesque scenery, and antiquities of the western counties of England, made in the years 1794 and 1796” by William Maton.