A Preliminary Investigation of the Layer Known as the “Head”

in the Glacial Tills of the Holderness Coast

By Graham Kings, Arthur Speed and Graham Evans,

Bisat Research Group of the Hull Geological Society.

Keywords.

Bisat Project, Withernsea Till, Skipsea Till, Head.

Abstract.

A preliminary investigation is reported of a layer of diamicton approximately 1 metre thick in the Withernsea Till on the Holderness Coast and described by W. S. Bisat as a “head”. A similar layer has been observed in the Skipsea Till in photographs taken as part of the Bisat Project, but not investigated in detail. The “head” exhibits many properties of the adjacent layers of Withernsea Till including particle size, colour and the clasts present, but differs in its weathering characteristics and texture. It is concluded that the “head” has a similar geographical origin to the Withernsea Till but differs in its deposition process or has undergone post-deposition changes. 

Introduction.

Between April 2015 and September 2019 the authors and other members of the Hull Geological Society, undertook the Bisat Project fieldwork, inspired by the work of W. S. Bisat who, during 1935–1939 and 1945-1952, examined, walked and sketched the cliffs from Easington to Sewerby (Catt and Madgett, 1981).

The HGS Bisat Project seeks to re-examine and photograph the Holderness cliffs from Sewerby (TA 19891 68464) to the end of the cliffs near to the Spurn Bird Observatory (TA 30869 32454), a total of 42 miles (66 kilometres). Much of the exposed coastal cliff comprises diamicton or till, a collective term, according to Allaby (2013), for the group of sediments laid down by the direct action of glacial ice without the intervention of water. During the photography project, which involved taking sequential overlapping photographs, an unusual phenomenon was noted comprising a 1-metre-thick recessed band of material of different texture running almost horizontally between layers of the diamicton (Fig 1).  

Fig 1. The Head at location TA 36006 25596 lying here between layers of the Withernsea Till.

While photographing the cliffs this band was recorded as an “earthy layer”. Later it was realised that this layer was the “head” identified by W S Bisat (1937) and described by Bisat, Penny and Neale (1962) associated with both the Withernsea and Skipsea Tills (formerly known as the Purple Clay and Drab Clay respectively).

Bisat (1937) referred to this layer as a “head”. However, this bed does not correspond to the modern definition of a head as “a sheet of poorly sorted, angular rock debris, mantling a hillslope and deposited by gelifluction” (Allaby, 2013; BGS Lexicon), nevertheless this paper will continue Bisat’s use of the term “head”.

Extent of the “Head” Exposure and Location of the Site Studied. 

A recent re-examination of the Bisat Project photographs revealed other examples of this “earthy layer” or “head” along the coast in both the Withernsea and Skipsea Tills. These exposures are listed in Table 1 and the coastal areas involved shown in Fig 2.   It should be noted that because of coastal erosion, typically 2m/year, the grid references reflect locations when the cliffs were photographed and are now off the current coastline.

[Table 1. Exposures of the “head” noted in the field during the Bisat Project

 and subsequently during examination of the photographs.]

[Fig 2. Coastal Areas where the “head” was visible in Bisat Project photographs.

Towns correspond to those listed in Table 1.

Circle O shows approximate location shown in Fig 1 and site studied (Fig 3).]

The site (TA 35816 25746), south of Withernsea, described in this paper is part of a continuous 2 km long exposure of the “head” from TA35056 26791 to TA36257 25284 representing the longest continuous exposure in the Withernsea Till. This site (Fig 3) was selected for study because it was within walking distance, between the tides, from the beach access at The Runnel (TA 36688 24681) and because the two layers of the Withernsea Till and the “head” layer could be easily reached from beach level. Several visits to the site were necessary, in 2022/2024 to survey the site and collect samples, because of the limitations imposed by tides and weather conditions.

[Fig 3. The section studied at TA  35816 25746 showing the “Head” and the Upper and Lower Layers of the Withernsea Till.]

Field Observations .

The lithology of the site is shown in Fig 3. The ”head”, a diamicton, lies between two diamicton layers constituting the Withernsea Till which for the purpose of this paper we have called the Upper Layer and Lower Layer. The Upper Layer is divided by a gravel layer and lies below a sand bed and soil. As is common on the East Coast, the site is being rapidly eroded by the sea and had formed a promontory allowing both sides to be examined.

[Fig  4. Field lithology log of section at TA 35816 25746].

As shown in Fig 4, the surfaces of the Upper and Lower Layers show vertical and horizontal weathering patterns while the weathered surface of the “head” resembles horizontal laminations. The surface of the “head” is eroded approximately 10cm more than the Upper and Lower Layers causing it to be recessed.

Samples from cleaned surfaces were compared with Munsell Charts and the results recorded and presented in Table 2 together with the maximum size of clasts, the response to a magnet and the reaction to 10% hydrochloric acid.

[Table 2. Field examination of the Tills.]

An attempt was made to measure the rheological characteristics of the tills using a strain vane gauge on both the north and south sides of the promontory. However, all readings were at or above the limit of the strain vane scale i.e. 1Kg/ cm² (see Table 2).   

Using the hand-held bulb planter described below a sample was taken from each layer and pushed out onto the beach (Fig 5). The texture of the core taken from the “head” was noticeably different from that taken from the Upper and Lower Layers. The cores of the Upper and Lower Layers were noted to be of a firm and moist consistency which could be moulded in the hands like putty. The “head” layer crumbled in the hand.

[Fig 5. Samples of tills taken with a bulb planter and pushed out onto the sand.]

Offsite Examination of Samples.

Collection of Samples.

Using a bulb planter corer, manufactured by Burgon and Ball of Sheffield, 6 cm in diameter and 16 cm long, further samples of the “head “and Upper and Lower Layers were taken for off-site examination. Difficulty was experienced when taking the sample from the Upper Layer because the same amount of force could not be exerted when reaching up.  The “head”, being softer and more friable, was easier to sample as was the easily reached Lower Layer. Therefore the same quantity of sample could not be obtained from each layer (see Table 3). The bulb planter was cleaned between each sampling to prevent contamination. The samples were placed in clean polythene bags and labelled.

Preparation of Samples.

On return from the field the samples were weighed and gently disaggregated using a pestle and mortar. They were then allowed to air dry before the dry weight of each specimen was recorded.

The sample was de-flocculated by boiling with a dilute aqueous solution of washing soda for 30 minutes and then wet sieved using a larger than 2.0mm sieve to remove large clasts followed by 125µm and 63µm sieves. The residual fractions of the samples were then air dried again and reweighed (Table 3). Each residue sample was stored in labelled test tubes.

In addition the 125µm to 2mm sample was dry sieved using a 500µm sieve in preparation for microscopic examination of the clasts. Reflecting the initial sample weights the dry sieving provided a 2.0g sample of the Upper Layer, a 4.0g sample of the “head” and a 5.0g sample of the Lower Layer.

[Table 3. Specimen weights and grain size distribution.]

Microscopic Examination of the Clasts.

The 500µm to 2mm sieve fraction samples of each layer were microscopically examined.  It was found that the clasts in the samples could be classified, based on their colour and lustre, to one of eight different clast types as shown in the first column of Table 4.  This finding was confirmed by experimental trial assessments across the layers and “head”.

The number of clasts of each clast type was determined by a team of two. One examined the sample scattered over a sampling tray using a x10 binocular microscope and verbally assigned each clast to a colour and lustre clast type. The second team member recorded the classification on a printed form which listed the eight clast types (Table 4). This method permitted the recording of many clasts in a relatively brief period before fatigue affected the observer. Approximately 1000 clasts were classified per sample.

Subsequently representative examples of the eight clast types were examined by Mike Horne, Secretary of the Hull Geological Society, who identified their mineralogy which is recorded in the second column of Table 4.

[Table 4. Microscopic examination of clasts.]

Fig 6 shows the proportion of each clast type in terms of its mineralogy for the Upper Layer, Lower Layer and “head”. It was found difficult for some of the grey rocks to assign them with certainty to a particular clast type. Therefore, the counts for the Granular / Grey White, Dull Grey and Sparkly Grey (Quartz mica rock, Coal or igneous rock and Grey sandstone respectively) were combined in Fig 6 

[Fig 6. Percentage of clasts in the Upper Layer, Lower Layer and “head”.]

Discussion

Determining the extent of a layer, such as the “head” in coastal cliffs is frustrated by the presence of slumping, vegetation, changes of elevation with respect to beach level and man-made interventions such as sea defences and war time installations. With this in mind, field notes made during the Bisat Project and subsequent examination of the photographs suggest that the “head” may be a near continuous layer south of Withernsea to Holmpton in the Withernsea Till and also present in the Skipsea Till as was found by Bisat, Penny and Neale (1962). 

Observations on the site, south of Withernsea, show the “head” and the Upper and Lower Layers of Withernsea Till have similar Munsell Colour, reaction to HCl, magnetic properties and maximum size of clast (Table 2). Sieved harvested samples of each of the three layers also show a similar percentage weight fraction of material retained on 2.00 mm, 125µm, 63µm sieves and in the clay/silt (<63µm) fraction (Table 3).

Recognising the limited resources available to the authors, microscopic examination of the 500µm sieve fraction suggests a similar percentage of clasts by number, classified according to colour and lustre (Fig 6) in the Lower and Upper Layers and “head”.

Erratics in tills are characteristic of their geographic source (Evans and Benn, 2014). Thus the above observations support a hypothesis that the material responsible for the “head”, has a similar geographical origin as the Upper and Lower Layers of the Withernsea Till found south of Withernsea. The Withernsea Till originated from Lake District ice before crossing the Pennines via the Stainmore Gap and overriding Skipsea Till ice from south-east Scotland and north-east England (Catt, 2007).

The “head” differs from the Upper and Lower Layers of the Withernsea Till in a number of ways:

·        In-situ the “head” is weathered back relative to the surfaces of the Upper and Lower Layers.

·        The “head” weathers to a pattern resembling horizontal laminations while the Upper and Lower Layers exhibit horizontal and vertical cracking.

·        The “head” crumbles easily whereas the Upper and Lower Layers mould like putty in the hand.

The observation that the difference in appearance was due to surface weathering was made by Rodger Connell (Connell, 2023 pers. cor.) while reviewing photographs taken as part of the Bisat Project. He noticed that when material fell away from the junction of the “head” and till, the head is no longer clearly defined; it needs surface weathering for the difference in the beds to become clearly visible.

The distinctly different properties described above, are not unusual for tills with the same composition since in addition to the gravitational forces during deposition they are subject to differing amounts of shear (Clark, 2018).  

The observation that the “head” has been seen in both the Withernsea and Skipsea Tills supports the view that the process responsible for their formation occurred at the site of deposition.

Mention has been made that the term “head” was used by Bisat, but that the bed investigated would not meet the modern definition of that term. It is interesting to speculate why Bisat used that term, other than it was at the top of a bed. Equally it could be that he was alluding to the process of deposition.

Conclusions.

This study has begun to explore a band of diamicton described by Bisat as “head” located south of Withernsea in the Withernsea Till. It is found that the “head” exhibits many properties of the adjacent layers of Withernsea Till including particle size, colour and clasts present but differs in its weathering characteristics and texture. It is concluded that the “head” has a similar geographical origin to the Withernsea Till but differs in its deposition process or has undergone post-deposition changes.

A band of diamicton with similar appearance was also been found in the Skipsea Till during the photographic Bisat Project.

The “head” exhibits different weathering patterns and texture to the surrounding till and further work is required both in the Withernsea and Skipsea Tills at other locations to explore these differences further. In particular it is believed that the use of a stronger shear vane might be informative. Further research is required to understand how different deposition processes and post-deposition environments influence the properties of tills.

Acknowledgements.

Mike Horne, Dennis Haughey and Roger Connell, other members of the Bisat Project.

References. 

Allaby M (ed) 2013. A dictionary of geology and earth sciences. Oxford University Press, USA.

Baretman M D, P C Buckland, C D Frederick & N J Whitehouse 2001. The Quaternary of East Yorkshire and North Lincolnshire.  Quaternary Research Association field guide, 218pp.

Bisat W S 1937. Reports of Field Meetings for 1936 (Hornsea). Proceedings of the Yorkshire Geological Society 23, 125-7, pl. vi.

Bisat W S, L F Penny & J W Neale 1962. Geology around the University Towns: Hull. Geologists’ Association Guides 11, 1-34. 

British Geological Society [accessed 24 March 2025].The BGS Lexicon of Named Rock Units – Head. Available at:

https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEAD#:~:text=Head%20is%20poorly%20sorted%20and,unsorted%20and%20unsaturated%20superficial%20deposits.

Catt J A 2007. The Pleistocene glaciations of eastern Yorkshire: a review. Proceedings of the Yorkshire Geological Society 56(3), 177-207.

Catt J A & P A Madgett 1981. The Work of W. S. Bisat FRS. Chapter 12, pp 119-136 of Neale & Flenley (eds) The Quaternary in Britain: Essays, Reviews and Original Work on the Quaternary Published in Honour of Lewis Penny on His Retirement, Pergamon Press.

Clark B G 2018. The engineering properties of glacial tills. Geotechnical Research 5 (4), 262-277.

Evans D J & D I Benn (eds) 2004. A practical guide to the study of glacial sediments. Routledge. 290pp.

 [paper submitted 13 May 2025 & published 1st July 2025]

copyright Hull Geological Society 2025