Stephen K Donovan (The Netherlands)
Wall games are a very geological form of light entertainment and education. I certainly have amused myself by identifying rocks and their features in walls since my days as an undergraduate and before. I was introduced to the name for the wall game (obvious, I know) by Eric Robinson (1996, 1997). Eric’s examples inspired me to devise my own version of a wall game in far-flung Jamaica. At the time, I was a member of the teaching staff in geology at the University of the West Indies in Mona, Kingston. Each semester, we took the first year classes for three one-day field excursions. As cash was getting ever tighter.
I hit upon the money-saving idea of running one of the first trips on campus where there were various ‘urban geological’ features worthy of note. One of these was the stone base of a ruined building that had survived from Mona’s days as a sugar plantation. The rocks in the base were a marvellous mixture of blocks and rounded boulders, presumably collected from the bed of the nearby Hope River, which drains the mountainous country to the east of the university. This trip worked well and, after a few years, the late Trevor Jackson and I published a field guide based on my excursion (Donovan and Jackson, 2000).
The primary criterion for a geologically interesting and educational wall game is a good variety of rocks. The Mona wall game was most satisfactory in this respect, with a mixture of sedimentary and igneous clasts and worked blocks, and even one specimens with a fault running through it (Donovan and Jackson, 2000, fig. 3D-H). But such diverse compendiums of rock types are rare because stone walls have commonly been built from a local source of rock, such as from loose boulders in a river or collected when clearing a field (Anon, 2002).
These are commonly composed of one type, that is, the rock that occurs in local outcrop (Nield, 2014). Yet I do not regard this as a problem – rather than searching for different rock types, you can still look for a variety of features shown by one or a few types of local rocks. For example, when on holiday in the White Peak of the Peak District of Derbyshire, I always examine the Carboniferous limestones of the dry stone walls for fossils.
Sedimentary structures are also an interest if mine, particularly trace fossils in walls (for example, Donovan, 2016, fig. 2H), but also physically- and chemically-controlled structures such as cross-bedding and nodules. This brings me to the Marriott Worsley Park Hotel and Country Club in Manchester. I first stayed in this most comfortable of hotels with my family in 2009 and have been back several times since. The main entrance is down a short slope with a car turning circle, flanked on one side by a slightly sinuous stone wall (Fig. 1). When the site was being rebuilt from its previous (derelict) agricultural origins into a luxury hotel (Redman, 1998), I presume that this wall was built from blocks and boulders already available on the site. In turn, these were likely to have been obtained locally when the original buildings were constructed. It is this wall and its wall game that I want to describe after my most recent visit.
The rocks that outcrop in the area local to Worsley Park are from the Upper Carboniferous (Pennsylvanian) Pennine Coal Measures Group, particularly the Pennine Middle Coal Measures Formation, and the Triassic New Red Sandstone of the Sherwood Sandstone Group, mainly the Chester Pebble Beds Formation (Crofts et al., 2012). The rocks in the Worsley Park wall (Fig. 1) are most probably derived from these units and are mainly Coal Measures. All rocks are siliciclastics, mainly medium- to coarse-grained sandstones, with some pebble conglomerates (Figs. 2 and 3). The principal mineralogy of the blocks is, where the surface is clean enough to see quartzitic (for example, Figs. 2B and 3E). The colours range from pale grey (perhaps ganisters; Tucker, 2011, p. 42) to a straw-brown (Coal Measures) to, less common, a deep purple-red (New Red Sandstone).
It is possible that at least some of the latter may include Carboniferous rocks that have been secondarily reddened (Crofts et al., 2012, pl. 3). Although boulders are cemented into the wall with bedding horizontal (such as in Figs. 2D, F, H and I, and 3) to tilted (Fig. 2B and G) to vertical (Fig. 2 A, C and E), I did not see any undoubted cross bedding. In some blocks, the direction of bedding is enhanced by the growth of moss (Fig. 2E). One boulder has a diagenetic development of a haematitic iron pan between bedding planes (for example, Fig. 2A and C).
Pebbles in conglomerates are either preserved in situ, mainly quartz with some rock fragments (Figs. 2E and 3F), or are mud ‘rip-up’ clasts that have been partially or entirely eroded away, leaving elongate holes in the rock (Figs. 2D, E and G, and 3G). Quartz and lithic pebbles are moderately rounded (Fig. 3F), suggesting that they have a history of fluvial transport. Sand grains are not well-rounded, but angular, indicating that they were not formed in the desert (Figs. 2B and 3E).
One thing of which I am confident is that, although I have spotted some interesting features in this wall, I have not caught them all. In particular, I failed to find any evidence of fossil plants in rocks that I have assumed were mainly derived from the Coal Measures. I invite those in the Manchester area to see both what I have described and to discover what I have not. I shall be back to add to my observations in the not too distant future, I hope. Whatever, this is one of the rare geological sites where I can be confident that there is a comfortable bar and restaurant close at hand in which to relax and reflect on my observations.
Anon. 2002. Dry Stone Walls: The National Collection. Dry Stone Walling Association of Great Britain, Sutton Coldfield, 64 pp.
Crofts, R.G., Hough, E., Humpage, A.J. & Reeves, H.J. 2012. Geology of the Manchester district – a brief explanation of the geological map. Sheet Explanation of the British Geological Survey, 1:50 000 Sheet 85 Manchester (England and Wales): 45 pp.
Donovan, S.K. 2016. Annual meeting of the Geological Society of America, Baltimore, November 2015. Deposits, 46: 9-12.
Donovan, S.K. & Jackson, T.A. 2000. Field guide to the geology of the University of the West Indies campus, Mona. Caribbean Journal of Earth Science, 34 (for 1999): 17-24.
Nield, T. 2014. Underlands: A Journey through Britain’s Lost Landscape. Granta, London, xvii+251 pp.
Redman, N. 1998. A History of the Marriott Worsley Park. Whitbread plc, 26 pp. [Available on-line at http://www.worsleycivictrust.org.]
Robinson, E. 1996. A version of ‘The Wall Game’ in Battersea Park. In Bennett, M.R., Doyle, P., Larwood, J.G. & Prosser, C.D. (eds), Geology on your Doorstep: The role of urban geology in earth heritage conservation: 163-170. Geological Society, London.
Robinson, E. 1997. The stones of the Mile End Road: a geology of Middlemiss country. Proceedings of the Geologists’ Association, 108: 171-176.
Tucker, M.E. 2011. Sedimentary Rocks in the Field: A Practical Guide. Fourth edition.
Wiley-Blackwell, Chichester, xi+276 pp.