Urban geology: boulders and the Dutch

My late wife, Dr Trina MacGillivray, was a geomorphologist. She loved the Netherlands and the Dutch landscape, but more than once made astute comparisons with the scenery of other northern European countries. The Dutch landscape, if it has a fault, is too organised, too well arranged and too manicured. Woe betide the blade of grass that dare step out of line. Trina’s observations extended to Belgium. If travelling to Brussels by train, it is immediately obvious when you have crossed the border because the landscape relaxes. It is not unruly or untidy, but, unlike the Netherlands, it does not need to maintain a near-geometric precision. Trina liked her trips to Belgium, too.

These memories were revived on a recent bus ride from Leiden to Hoofddorp, near Amsterdam Schiphol International Airport. It was a grey, overcast day – the sort of dreary weather that the Netherlands does too well and too often. Even before we had left Leiden, the regular geometry of the town impressed itself on me. But then there was something in the central reservation that caught my eye – a cluster of irregularly rounded boulders of various lithologies (Fig. 1E, F). It occurred to me then that such clusters of boulders were not so unusual in the Dutch landscape, breaking up the geometry in unusual ways (Figs. 1 to 3), yet were undoubtedly man-made.

Fig. 1. Boulders in Leiden, 4 February 2015. (A) The boulder garden, a favourite of all children who like to climb, outside the Naturalis Biodiversity Center. Note the footbridge in the background, which looks like a rack of giant ribs from a primordial behemoth. (B-D) The turning circle at Leiden University Medical Centre (LUMC). (B) A general view, with the hospital to the left and the railway on the right. (C) Part of the sweep of boulders and cobbles closest to the photographer in (B), showing something of the lithological diversity. (D) Most boulders are crystalline or nondescript sandstones, but rare boulders of red bed (Permo-Triassic?) conglomerates make an attractive change. (E, F) Two views of angular boulders in the central reservation in Willem de Zwijgerlaan. These appear to be entirely decorative, as nobody would want to park in the middle of such a busy road.

Noël Coward said “Very flat, Norfolk”, yet, with major glacio-tectonic features like the Cromer Ridge (Bridges, 1998, pp. 44-48), the county has a positively hilly topography compared to most of the Netherlands (but, to be fair, Coward might have had something else in mind as well). It is not an exaggeration to say that, apart from sand dunes, the north and west of the Netherlands are far flatter than any of the so-called ‘flat’ eastern English counties bordering the North Sea. Most of the Netherlands is mantled by thick, unconsolidated Holocene and Pleistocene deposits (Meijer, 1985, pp. 6-7; Zagwijn, 1985). For example, much of my bus journey from Leiden was on an ancient lake bed, drained a little over 160 years ago and flat as the proverbial Dutch pancake. The high Netherlands is in the far southwest of the country and reaches the highest point of just over 320m at the triple border with Belgium and Germany. This is only slightly higher than the North Downs.

Exposures of in situ rocks or rocky road cuttings are seen only too rarely in the Netherlands. There are just not any rocks to expose or cut through, except in the east and south. A flat topography without hills of ancient rocks has meant that roads and railways just follow the landscape in any direction they want. To break up the monotony of such flat lands, here and there, imported boulders have been introduced as upstanding features, particularly in urban settings (Donovan, 2014a, b). These man-made structures may imitate natural features elsewhere (such as Fig. 3A) or may be extraneous to the normal architecture and geometry of urban and industrial landscapes. They are also most welcome to the eye of the geologist.

Other boulders occur in clusters and obviously serve a purpose – dissuading motorists from parking on patches of ground that would otherwise be unoccupied and tempting. Such vacant spaces are easily occluded by boulders, either regularly spaced at the curb-side (Fig. 2A-C) or piled up to form a more robust barrier (Fig. 1B, C). Both are more satisfactory to the eye than some metal barrier. Some of my favourite boulders are in the turning circle for heavy delivery vehicles between the Leiden University Medical Centre (LUMC) and the railway at the Den Haag (The Hague) end of Leiden Central railway station. Most of the boulders are crystalline (igneous and metamorphic) of well-indurated sandstone, but the LUMC turning circle has rare, well-rounded boulders of red bed conglomerates (Fig. 1D), presumably from the New Red Sandstone (Permo-Triassic).

Fig. 2. Boulders in Hoofddorp, 31 January 2015. (A, B) McDonald’s cafe, on the corner of Vuursteen and Kruisweg. (A) A general view of boulders protecting a small area of grass from errant car parkers. (B) A detail of three boulders. From top to bottom: granitic igneous intrusive rich in K-feldspar; nondescript block of (probable) sandstone; and a schist. (C) Line of angular, Carboniferous limestone boulders in Siriusdreef, looking northeast towards Polaris Avenue (compare with Donovan, 2014a, fig. 2) – again, a discouragement to errant parkers. (D-F) Boulders at the end of Siriusdreef behind the photographer in (C). (D) Boulders enclosed in a topiary of box – without intending any pun, they look like chocolates in a giant chocolate box. (E) Up the steps and behind the topiary, yet more boulders on a bed of limestone chippings (and snow). (F) A detail of a massive boulder, right of centre in (E), showing two directions of quartz veins in a massive sandstone(?). The top-to-bottom veins cross-cut those from left-to-right; the latter are therefore older.

The Naturalis Biodiversity Center (the national natural history museum) is the other side of the LUMC. Here, there is a kid’s playground with a difference, with boulders forming climbing frames (Fig. 1A).

Some Dutch gardens may appear barren to the British eye. The principal purpose sometimes seems to be, not so much to grow plants, but to subjugate nature. Pavements and slabs are the order of the day, with a few plants imprisoned in pots or minimalist flowerbeds, often in raised beds. Many gardens are so botanically-challenged that I imagine the gardener taking their inspiration from the Borg in Star Trek: ‘Resistance is futile’. Into these semi-deserts, rare boulders, cobbles and slabs of rock make a sparse change (Fig. 3B, C). These are natural objects, like plants, in an otherwise unnatural environment. They are not there to entertain wandering geologists such as myself (but they do, nonetheless) but, rather, are presumed to be natural additions that need less maintenance than a plant, apart (perhaps) from an occasional splash of bleach to clean off any moss or algae.

Fig. 3. Boulders in Hoofddorp, 7 February 2015. (A) The southwest bank of the Recreatieplas Toolenburg, a man-made lake, armoured by boulders of Carboniferous limestone. This is largely decorative, as the lake level varies little and only the strongest North Sea gale produces waves that are potentially erosive. (B, C) Boulders and cobbles in a front garden in the Graan voor Visch area. On one side of the garden, the slabs are all Carboniferous limestone (B), whereas on the opposite side, they are a mixture of lithic cobbles. The photographer is standing on the pavement.

Bridges, E.M. 1998. Classic Landforms of the North Norfolk Coast. Geographical Association, Sheffield, 52 pp.

Donovan, S.K. 2014a. Urban geology: A sunny Sunday in Hoofddorp. Deposits, 38: 8-10.

Donovan, S.K. 2014b. An unnatural bridge in an artificial limestone environment, the Netherlands. Cave & Karst Science, 41: 118-119.

Meijer, H. 1985. Compact Geography of the Netherlands. Fifth impression. Ministry of Foreign Affairs, The Hague, 43 pp.

Zagwijn, W.H. 1985. An outline of the Quaternary stratigraphy of the Netherlands. Geologie en Mijnbouw, 64: 17-24.


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