The Agglestone is described here:
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'The Agglestone was until recently a type of pedestal rock, but it has since fallen towards the southeast. It was an anvil-shaped block of about 400 or 500 tons weight, perched on a conical hill which the stone has protected from the weather. It is an eroded relic of iron-cemented, Tertiary sandstone, the Agglestone Grit. This is a coarse, cross-bedded and pebbly grit of Eocene age of about 11 metres in thickness,and it takes its name from the rock. The ferruginous sandstone is not confined to the Agglestone but also forms the Puckstone nearby and, in addition, pieces of this hard irony sandstone litter the heath and have been used for building walls, barns and houses. The Agglestone rock, is, needless to say, not a sarsen stone nor something put in place by man. It is, nevertheless, a rather unusual and interesting hill-top tor.
There is no direct road access to the Agglestone, but there is a pleasant walk to it. Consult the Ordnance Survey map - Purbeck and South Dorset - Outdoor Leisure Map 15, 1:25,000. The location of the rock is northwest of Studland village at map reference SZ 023828. There are several paths from the village and also one from Dean Hill. Park a car at one of the two National Trust car parks at Studland or at Knoll Beach. One route is to walk to the Knoll House Hotel on the road north of Studland village. There is a black gate on the west side of the road just south of the Hotel (mentioned in the old account in the footnote below). Pass through this, cross a field, past a house and then down a farm track to the ferny valley, thence westward, and then southwest onto the heath, where the rock stands out conspicuously on a hill. It is really not far from the village but the place seems quite remote, and much like a tor on Dartmoor.
The characteristics and lateral relationships of the Agglestone Grit has been discussed briefly by Arkell (1947). It is not only exposed in the Agglestone. It also has been seen in a sandpit near the golf course and in pipe-clay workings at Newtown. Arkell commented that westward it and the upper part of the Pipe-clay Series contain an increasing amount of pebbly beds, composed of flint, Upper Greensand chert, vein-quartz, and far-travelled Palaeozoic detritus (of Cornubian type), together with small pieces of silicified Purbeck limestone. In this condition the strata are the typical "Bagshot Beds" of the Moreton and Warmwell district. Westwards they overlap the two lower members of the "Bagshot Beds" and the London Clay until between Warmwell and West Stafford they rest unconformably on the Reading Formation (of the Thames Group). Finally in the outliers south and southwest of Dorchester they consist mainly of shingle and coarse cobble gravels, in a matrix of typical Agglestone Grit, let into huge solution pipes let into the Chalk.
Thus the detritus indicates a Middle Eocene river flowing east from Cornubia (the old Devon and Cornwall upland) onto the Bournemouth delta. The westward overstep shows that eastward tilting was taking place, and this was at about the same time as the earliest "Alpine" movements were produced by a north-south compressional regime. The pebbly grit of the Agglestone is likely to be a channel deposit of the river situated on the delta. The river was flowing sufficiently fast to move this fairly coarse material and, furthermore, it was also carrying Fe from the chemical weathering on the uplands (to be expected from the Eocene palaeoclimate). The current cross-bedded channel debris was, in due course, cemented by hydrated iron oxide - limonite or goethite. The cementation was greater at this particular point, for a reason not known, and the relatively resistant rock material was produced. In relatively recent times there has been erosion and the softer, more less-resistant sediment around the Agglestone was washed away, leaving a prominant rock. This may not necessarily be the complete explanation though because the Agglestone is undercut around the sides in a rather unusual manner.
A more specific reason for the shape has been postulated by Hardy (1910). He noted that the rock is of sandstone resting on its natural bed and is on the northeast of of a 0.8 km ridge of "Bagshot" sandstone. It stands on a steep, semi-circular mound about 27m above the bog below. The depression has formed a natural receptacle for the debris was has been washed or fallen from the sandstone ridge. He considered that this ridge was once a vast quarry, especially at its east end and the present Agglestone rock is a relic left after the excavations had terminated. The ancient masons cut doorsteps, walling stones and handmill stones etc from the Agglestone Grit. He had found a fine example of an Agglestone Grit doorsill under the foundations of Studland Church during restoration. It was rebated and had one square hole for a jamb and two or three for iron bolts. Hardy considered that the Agglestone Rock waqs undoubtedly once much larger than it is now, perhaps about four times its present size when it was left by the quarrymen. The top crust consists of very hard, ferruginous sandstone, about 2 m thick with natural joints running perpendicularly through it at varying intervals. The bottom strata is softer and kept moist by rain, mists and drippings from the rock above. After the quarrymen had left it natural weathering operated on it, including the effects of frost-wedging. Rains wash portions of the softer substratum away and in addition when a dry wind blows the chipped rock is blown off. Pedestal rocks in deserts have in many cases been attributed to wind deflation and abrasion. The Agglestone does not seem to directly affected by the blown sand abrasion because although the sand dunes of the South Haven Peninsula are not close to the rock which has boggy moorland adjacent. The Agglestone has been undermined by up to 1.2m on the north side and 3.7 m on the south side. Hardy made comparison between this rock and the rocking and logan stones of Cornwall and elsewhere. He noted that frost cracking of the hard top part has forced off lumps of rock from 5 to 15 tons weight and found 23 large pieces around the mound when he examined it. Hardy predicted its collapse, which has since occurred.
There is a complete lack of carbonate in the Eocene strata in the vicinity of the Agglestone. Water is held up in places by clays. The result is the occurrence of acid and peaty bogs like those of much of the New Forest. The bogs are treacherous and walkers should stay on the footpaths. Within the soft, wet ground of bogs the small, insectivorous plant Sundrew or Drosera, occurs as in the New Forest bogs. This obtains nitrogen from flies. Some of the other plants of the Agglestone walk are mentioned in the old account given in the footnote below. Most of these are still there, although the Osmundia ferns did not seem very tall at the time of my recent visit. Please take care not to disturb or remove any plants, so that the Agglestone geological and botanical walk is still as good in another 100 years time!'
We have enjoyed many walks in Godlingston Heath and Studland Heath past The Agglestone and always wish to return to this beautiful area.