3D Lidar landscape on Sketchfab: https://skfb.ly/pLzuM

This recent post on the LiDAR and Aerial Archaeology Group of Facebook sparked my interest.
https://www.facebook.com/groups/1508789132952429/?multi_permalinks=2398701490627851

The post describes an apparently circular enclosure revealed in the lidar dtm on the summit of the small wooded island in the centre of Grasmere lake. The author of the post suggested it might be prehistoric, and previously unrecorded.

Enhancing the lidar using a local relief model certainly shows a feature there which I was quick to confirm by that and other enhancements. The author suggested it shows a bank, a ditch, then another bank enclosing a sunken hollow at the top.

I still have doubts (and feel much less certain than 50:50) for reasons I will hopefully explain below. That said, the only way to be sure that this is something or nothing is a ground-truthing visit which perhaps the National Trust archaeologists will manage in the future. My reaction to these things is to explore the topography in as much detail as I can. Visitors to the island are not currently allowed so only remote methods are available. 

I can certainly confirm that there appears to be something shown on lidar images (here I call it a 'doughnut') on the south end of Grasmere Island. It appears to be approximately 50m in diameter, apparently enclosing the summit. 

The two images below are my favourite and most used methods of enhancing lidar images for archaeology use.

Feeling the need to explore the topography of the island (and this feature/anomaly) in more detail I had a look at the 3D visualisations which you can derive from the lidar data in several ways using QGIS. One of my favourite ways is using contours, here overlaid on a multi-directional hillshade.

From the level of the lake (about 61m above sea level), the south end of Grasmere Island rises to a peak (75m ASL) which occupies a broad ridge running NE-SW from a slightly lower second summit on the N part of the island. With a contour interval of 0.5m, the 14m between the water level of the lake and the summit are modelled by 28 contour lines which closely define the shape and altitude of the island and show us where the slopes are steepest.

A second ridge runs steeply down from the main summit SE towards the lake where a building is indicated on the map (locally described as a barn). It is the site of William Wordsworth's poem: Inscription for the House (an Out-house) on the Island at Grasmere.

The question I pose is: does the lidar show ditches and banks encircling a summit (perhaps a small fortified enclosure) or something more natural?

Below using the elevation profile tool showing a section across the southern summit. This suggests a series of steps, about 2m high to the NW of the summit and they certainly don't model a doughnut ring or hollow centre. There are hints of small valley features running along the hillside just below the lower step on the W and NW sides, but these don't continue round the contours on the steep E side.

You can clearly see the two upper steps or ledges in the elevation profile shown below.

Using a contour interval of 0.1m (perhaps pushing the resolution a little too far) I believe we can duplicate all the elements of the island doughnut, apart perhaps for the ditch (if that is what there is) which lies just below the second steep slope NW of the summit ridge. The contours confirm what we see using a slope analysis from lidar. In this representation, the steepest slopes are rendered as black, and flatter areas as white and lighter shades of grey.

The same of course can be demonstrated in a 3D model but is best when you can look yourself rather than on a screen capture from a single angle screenshot as shown below. The interactive model from which this screenshot was taken is freely available on Sketchfab and doesn't need to be downloaded.

Does any of this prove that the features are natural rather than man-made? Maybe not, but they give me huge doubts that only a ground observation can confirm.

If the feature is of natural origin then how might it be explained?

The contour model suggests to me something called trap topography - a step-like landscape formed by layered volcanic rocks. It occurs when alternating layers of hard, erosion-resistant lava and softer, crumbly volcanic ash weather away at different speeds. The hard lava forms steep cliffs (scarps), while the soft layers form flat shelves (benches), creating a natural staircase. There are certainly hints of this in the neighbouring hills and it is well known in the volcanic hills of the Lakes. I think similar features are visible, for example, in the area around Hardknott Roman Fort.

There is much geological data about this area of the Lake District here:
https://webapps.bgs.ac.uk/memoirs/docs/B01517.html
I can find little information about the topography and geomorphology of Grasmere Island itself, although a volcanic origin does appear likely.

Is what we are seeing in the lidar here a small scale version of trap topography along with some natural drainage? Now I wonder: what are those three small mounds at the N end of the island, NW of the southern summit?

My thanks to Adam Ibbotson for spotting this feature and for an interesting and stimulating post. They happen very rarely on Facebook. The analysis and interpretation here are of course my own.

The three images below show contours at interval of 0.5m created in QGIS from dsm lidar.

To enable further exploration of the Lowther Castle Estate I created a 3D Lidar landscape model on Sketchfab.

Today I am looking at the extensive parkland around the ruined mansion of Lowther Castle.

Wikipedia: Lowther Castle

Historic England Grade II Listed: 1000668

At the southern end of the estate, enhanced DTM lidar highlights two mounds (in white) surrounded by ditches (in black) located in grassland, just S of a large (perhaps recent) pond. The mounds are about 15m in diameter and about 0..5m high. They look very like Bronze Age burial mounds (tumuli or barrows). But are they a bit too neat to be prehistoric? The Historic Environment Record describes them as: "Possible ring ditches (circular or near circular ditches which may be the remains of ploughed out round barrows, round houses, or of modern features such as searchlight emplacements) of unknown date that appear as crop marks."

It also provides an alternative explanation for the features as old circular coppices, apparently "shown on a map of probably 18th century date kept in the Lowther Estate Office that when Lowther Castle was rebuilt in 1809 the Landscape Architect would have been of the opinion that the older circular coppices detracted from the newly-planted avenue as it appears from the Castle window".
Lake District National Park HER: 5375

There are several such circular ditched features in the northern part of the estate but they are nearly all of larger diameter and without raised central mounds. They look much more like tree planting rings than these do.

The two features shown near the pond are some 2.5km SW of the ruined mansion, nowhere near planted avenues, and blocked from line of sight by much higher land. If they really appear on the 18th century map as tree rings there would be no doubt. There is no hint of rings on the 1st edition OS map (c.1860) although that map suggests the pond may have been created on a site of clay extraction used by a nearby tile works. Evidence suggests that the features have been there for some time. Perhaps, rather than for tree planting, they are just fake archaeology created as special features within the parkland. They would certainly have been visible approaching the castle on Emperor's Drive from the former lodge on the A6.

On the prehistoric side of the argument, an archaeology report of part of Lowther Park by Oxford Archaeology North published in January 2005 states that "... the earliest identified activity within the vicinity of the park is from the Bronze Age: there are a pair of round cairns just south of the park Round Hill (NY 541 219)".
Gajos, Hannah (2005) Lowther Deer Park, Cumbria. Archaeological Survey and Evaluation.

Below lidar image (using DTM to remove trees) to compare the two mounds with several probable ditched tree-ring plantation features in the area of Lowther medieval village and the Castle Stead (Castlesteads) possible ring-work situated just north of the ruined mansion of Lowther Castle.

Includes St Michael's Church, Castle Stead (a possible Norman ring-work castle) and the deserted medieval village of Lowther, all situated north of Lowther Castle (the name of the ruined mansion house) above a steep bank above the River Lowther. Note that the several perfect circular ditched enclosures are likely former tree ring plantations often overlying earlier features.

The earthwork called Castle Stead is a rectangular ramparted enclosure 30m by 25m with very substantial ramparts 4-5m thick standing to 3m in height. The rampart is much thicker in the SE corner, possibly being the location of a tower. There are two possible entrances, one in the south and the other in the east. The predominantly earthwork form of the structure, the paucity of collapsed masonry and the possible twelfth century date would suggest that this was not a peel towe and is too small to have been a motte and bailey, but could have been a timber ringwork castle.
"The ancient village of Lowther was heretofor considerable, consisting of the hall, the church, the parsonage house, and seventeen tenements, messuages, and cottages, all of which were purchased by Sir John Lowther, in the year 1682, and pulled down to enlarge his demesne and open the prospect of his house, for they stood just in front of it’.

Wikipedia:Castle Stead

Gatehouse - Castle Stead, Lowther

Lancaster University: Lowther Medieval Castle and Village

Castle Studies Trust - Geophysical survey and excavation (2023)


3D Lidar landscape on Sketchfab:
  DTM: https://skfb.ly/pK9Ls
  DSM: https://skfb.ly/pK9KR

Cerne Abbas, Dorset.

Location: ST 6667 0168

Scheduled Monument: Hill figure called The Giant

Scheduled Monument: Earthworks on Giant Hill

National Trust Archaeology Record: MNA138903

Hill figures are unique to England and are found on the chalk scarp slopes across southern Enland with a few outlying examples in Yorkshire. Most of the figures are horses or military badges but there are two human figures, the Long Man of Wilmington (E Sussex) and the Cerne Abbas Giant.

The Giant is a 55m high chalk-cut figure, picked out in regularly replaced chalk, standing on the SW steep slope pf Giant Hill (Trendle Hill) above the viallage of Cerne Abbas and its abbey. The Giant carries a club in his right hand and has been called "Britain's most famous phallus" although some evidence suggests he wasn't always depicted without clothes.

There has been much speculation among antiquaries and archaeologists regarding his age, identity and meaning. The first known historical refernce is to a repair of the Giant in 1694. There is no mention of the figure in earlier records, notably a 1617 survey of the area by John Norden, who was famously thorough. There have been speculation that the Giant may have been constructed as far back as the prehistoric, with other theories suggesting Roman, early or late medieval periods.

Since 1920 the Giant has been in the care of the National Trust. The small excavations undertaken in 2020 were designed to collect samples of snail shells and soil at various layers of his construction which could provide accurate dating evidence. Quartz grains retrieved and kept in the dark can be dated using OSL (optically stimulated luminescence).

Examination of snail shells suggested the hill figure is "medieval or later". Snails dating only from the Roman period (brought from France as food) were not found at the site, while species first found in England from the 13th and 14th centuries were found. The OSL study yielded a date range for construction of 700–1100 CE in the early medieval to late Anglo-Saxon period.The discovery  was featured in Series 9, Episode 5of the BBC series Digging for Britain.

National Trust SW Archaeology blog:

   Dating the Cerne Giant Results!
   
   Cerne Giant the OSL dates

Below the specially flown drone over the Giant and adjacent area to get a good LiDAR survey of his earthworks (Downland Partnership).

3D lidar landscape on Sketchfab: https://skfb.ly/pHFJL

Wikipedia: Cerne Abbas Giant

https://historicengland.org.uk/research/results/aerial-archaeology-mapping-explorer/

Find area of interest using ST666016 in a grid reference search.

Styford (Bywell) [NZ 01556249] Mound. (1)

A large, artificial conical-shaped mound with a strong ditch surrounding on three sides. On the south there is a steep, natural slope to the river valley below. The mound is 5m high on the east, and the summit slopes slightly upwards to be 6.6m high on the west. The ditch is deepest and widest on the north where the approach is from higher ground. The whole earthwork has been mutilated by much quarrying. Rig and furrow ploughing runs up to the perimeter of the ditch. There is no apparent outer bank. Situated with a commanding view to east, south and west, the earthwork is defensive, and is quite characteristic of a motte. (2)

Description and published survey (25 inch) correct. (3)

Styford motte was built in the 12th century, and was the caput of the Bolbec family. (4)

Reference number: N10057

Henry I granted the lands here to Walter de Bolbec (d c.1133), which remained with his descendants until 1262. He may have founded the castle. This is one of the suggested sites of the castle of Tiefort, which was mentioned in 1216.

Gatehouse Gazeteer: 2445

Is there a faint outline of something in the flat field just N of the Styford Motte (NZ 0166 6273)? Very difficult to make this into anythying other than perhaps a possible plough-levelled enclosure, or lumpy, disturbed ground. It is visible on both dsm and dtm lidar. However, I have been unable to find any further evidence to support the observation such as crop-marks on available aerial photos or historic satellite imagery. The Historic England aerial mapping explorer is still blank in this area.

The trouble with this theory is the presence of even fainter and similar marks in the surrounding fields and nothing particularly representative of a deserted medieval village that we see elsewhere in Northumberland.

See K2P: N10068 

Wrathmell, S, 1975 is given as reference 6 and is quoted in the HER record as follows:

There is a similar 'disturbed' area visible on lidar between Styford Hall (built c.1800) and the old ford across the River Tyne within the emparked area (NZ 0200 6199). This could be the location of the buildings referred to on the 1708 and 1749 plans. Being close to the river, it would certainly have sufferered in the Great Flood of 1771.

Wrathmell could have been correct though in assuming that the early medieval deserted village was much higher above the river haughs, somewhere up near the motte.

There is little remaining medieval rig and furrow in either of the two locations although a small area can be seen on lidar running up to the NE edge of the ditch surrounding the motte.

Castle Hill, Haltwhistle, Northumberland.

Location: NY 7114 6416

"Castle Hill is a prominent, probably natural mound located towards the eastern end of Haltwhistle and a little way to the west of the steeply incised Haltwhistle Burn. It has long been considered a motte (Hodgson 1840, 117-18; Hunter Blair 1944, 164; Long 1967, 114). The western side of the mound certainly appears to have been artificially scarped and it is topped with a bank between 0.9m and 1.2m in height which today survives around the north and east sides.

This would seem, morphologically, to make it a ringwork rather than a motte. Despite much conjecture, little has been determined about the detailed chronology of these earthworks, and the mound is, today, quite severely impacted by development.

An archaeological watching brief carried out in 1992 when foundations were dug for an extension to Brae Bonny House, which lies against the mound, recovered one sherd of green-glazed pottery. The monitoring archaeologist concluded that the site had been levelled at some previous date and also established that an earlier extension of an adjacent house had required excavation deep into the mound, revealing 'several layers of stratigraphy'.

Hodgson conjectured that Castle Hill was the site of the medieval court for South Tynedale, as Wark-on-Tyne was for North Tynedale (1840, 119), but this does not appear to be supported by any documentary evidence, which is relatively plentiful for the role of Wark in this function. Indeed, in 1290, an inquiry into the death of a man in Haltwhistle resulting from a quarrel in the town was heard at Wark before the Bailiffs of Tynedale (Polson 1902, 74), presumably meaning that there was no court at Haltwhistle to carry out this function. (Northumberland Extensive Urban Survey)

Probable early Norman ringwork castle partially surviving as an earthwork."

Gatehouse: 2582 

Castle Hill possible motte and bailey (Haltwhistle)

[NY 71126416] Camp. (1)

Castle Hill is a natural mound cut off to the north east by the Haltwhistle Burn glen. Its west end has been scarped and a breastwork 3-4ft high added, which continues on the north and east sides. The probable site of a motte and bailey. See illustration card. (2)(3)

Published survey (25 inch) revised. Modern development has destroyed much of this earthwork, but a substantial earthen bank remains on the east side. No trace of a motte survives, and it is doubtful if one existed, the remains being more likely those of a simple breastwork around the summit of the hill. See AO/56/363/8. (4)

Haltwhistle Burn. Castle Hill once used as a motte and bailey castle. Traces of scarping and an earthen mound or wall can be seen. (5)

Watching brief carried out when foundations for an extension to Brae Bonny house were dug in August 1992 (application 92/E/13). The site appeared to have been levelled in the past and only one sherd of green glazed pottery was found. Inspection of the adjacent house revealed that an extension had been erected some time in the past and that it had gone deep into the hill. Several layers of stratigraphy had been evident. (6)

Castle Hill. (7)

Name of Haltwhistle owes its origin to the oval shaped mound called Castle Hill, which was once fortified with earthworks. (8)

Castle Hill was at some remote period defended by a system of earthworks. The base of the hill was formerly swept on the south side by the South Tyne; but the river has altered its course and does not now approach within some distance of the mound. (9)

The feature described above was obscurred by trees on all air photographs available to the Hadrian's Wall NMP project, so no determination of the survival or function of the features could be made. (10a)

Keys to the Past: N6684

Classified as Earthwork Enclosure by Cathcart-King (1983, 3340).

Geograph - Dally Castle

Dally Castle, Tarset, Northumberland.

Location: NY 7748 8438

Contour models from lidar

Shown below are contours created in QGIS at 1m interval from the dtm lidar, overlaid on the multi-hillshaded dsm lidar.

Below that are two profiles created by the profile tool in QGIS.

The first, in the direction NW-SE, shows the deep ditch dug across the ridge cutting off the site of the castle from the ridge to the west. It seems to suggest that material from the ditch was used to increase the height of the castle mound.

The second profile from NE-SW across the castle mound shows the ditch with outer rampart on the N side of the castle and the steep slope to the S into the flat haugh-land above the Chirdon Burn..

The remains of a fortified house, later remodelled as a tower house, of medieval date, situated on the summit of a ridge within a meander of the Chirdon Burn. The upstanding remains are Listed Grade I. The site of the fortified house has been isolated by the digging of a substantial ditch, 25m wide and a maximum of 4.5m deep, across the north western part of the ridge, and by a less substantial ditch
across the south eastern side. Natural protection is afforded on the north east and south western sides by steep slopes. The fortified house, which is situated between the two ditches, is visible as a rectangular structure measuring 20.9m north west to south east by 11.8m north east to south west, with walls of regular sandstone blocks 1.8m thick. This building is thought to be early 13th century in date and its basic plan is an upper floor hall house above a columned basement.

Each of the long side walls had three regularly spaced arrow loops, or narrow windows, and each of the end walls had one loop placed centrally. All of the windows were blocked soon after building and in the south west corner of the
house two of the windows have been obscured by an internal cupboard and a fireplace. The most westerly window in the south wall was subsequently replaced by a larger window, still clearly visible.

In the later 13th and 14th century the house was remodelled into a tower house and a number of features were added; these include a square tower at the north west corner, a tower at the north east corner, a pair of butresses on the north wall and a small tower at the south west corner. It is also thought that an entire storey was added.

A pair of buttresses added to the south wall of the house are thought to be an even later addition. The original entrance to the house is thought to have lain in the eastern end of the south wall, although there i s now only a gap in the masonry.

The foundations of a rectangular building, orientated east to west and measuring 9m by 6.4m, are located 10m east of the house. The building is thought to be the remains of an associated chapel. Further to the east of the house, on the eastern side of the smaller ditch, there are further slight foundations of a small building 3m square.

Dally Castle is believed to be the building erected by David Linsey in his manor of Chirdon, referred to in a document of 1237 as the `house with remarkably thick walls in the form of a tower'. The manor was confiscated on two occasions in 1289 and 1296. On the second occasion it was granted to John de Swinburne, reverting to the Crown on his death in 1326 when it was described as ‘the site of a manor burnt by the Scots'.

The fortified house is not mentioned in the 1415 or the 1541 lists of Border strongholds but it is known that by 1604 it was held of the Crown and occupied by the Dodds family. The condition of the house deteriorated; by the 18th century it was roofless and in the early 19th century little stonework was visible.

The building underwent limited excavation in 1888 when a series of columns forming part of the basement were removed. The work also uncovered a helmet and part of a sword. After substantial consolidation in the late 20th century, the walls are visible standing to a maximum height of 1.8m. Further columns and other architectural fragments were also uncovered and remain at the site. [NHLE].

Scheduled Monument List Entry Number: 1018537

Listed Building (Grade I): 1044856

Keys to the Past: N7045

Tarset Archive Group: Dally Castle A0284

Gatehouse - Dally Castle

Wikipedia - Dally Castle