3. The Collection of Erratics in the 19th Century and Later

Cummins's dismissal of Harmer's map of erratics in 1977 and 1979 came as a serious setback in my campaign to persuade prehistorians that knowing about all potential resources was vital before theories of trade or exchange were promoted (Cummins 1977; 1979). It was clearly important to find out what data Harmer had plotted and where they had come from. For this, I had to delve not only into the records of glacial observation in 19th-century Britain, but also to learn something of the structure and organisation of contemporary science.

Interpretational theories prosper, develop or wilt within appropriately accommodating, critical or hostile climates of belief. Until so many British universities were established between the two Great Wars in the 20th century, the world of learning was largely, though by no means exclusively, the domain of non-professional investigators.

As the 19th century progressed, hungry for learning and concerned to examine problems of Biblical theology and early traditions, the rising middle classes were particularly curious about natural history, geology and archaeology. Consequently, scientific investigations were carried out by industrialists and professional people: teachers, clerics and lawyers. Most were driven by curiosity; some were also collectors but, importantly, the pursuit of knowledge brought together disciplines that have since become separated. So the interested public often benefited from detailed media reporting on cutting-edge investigations about a wide range of scientific topics. In this way the idea of prehistory developed alongside other infant disciplines of science. Glaciology had serious implications for appreciating the long time-depth of human antiquity, particularly after the 1850s. So those concerned with human antiquity at that time were awake to the progress of nascent glacial studies.

While the appearance of Darwin's Origin of Species in 1859 revolutionised the world of natural history, that year was also an important milestone for prehistory. Having examined a section of the Somme gravels near Abbeville that year, Sir John Evans and Sir Joseph Prestwich returned to Britain and pronounced that they had seen (what are now known to have been) Palaeolithic tools embedded in strata alongside extinct mammals. This confirmed the long time-depth of human antiquity and raised questions about deposits apparently formed in glacial times. Their observations offered new dimensions to a growing public curiosity about the age, nature and extent of glacial events which, after much discussion and debate, were slowly replacing the notion of a Noachian Flood (Briggs 2007, 244-51).

But how best might the emerging notion of blanket ice-sheets be understood and be brought to a wider public? One way was to encourage people to observe, if not discover for themselves, the whereabouts and nature of glacially carried stones and ice-scratch marks on exposed rock surfaces. And that is what happened. Boulder-watching clubs were formed that became incorporated into the tradition of collecting specimens outdoors by members of long-established natural history societies.

Consequently, mainly between 1870 and 1914, tens of thousands of erratics were examined macroscopically by curious Victorian gentlemen and ladies, keen to find evidence for an Ice Age. The Royal Society of Scotland took the lead from 1871 to 1881, then The British Association for the Advancement of Science (BAAS) formed its own Boulder Committee which met annually from 1873, presenting analytical reports of the boulders observed by local groups, until such activities were eclipsed by the First World War.

The existence of such a regular forum and publication outlet by the BAAS stimulated the founding of boulder-watching groups all over northern England, particularly in Yorkshire, Lancashire and Lincolnshire. For a brief time, two English-language periodicals were virtually dedicated to describing erratics. These were The Naturalist (1875-) and The Glacialists' Magazine (1893-97).

This all had considerable bearing on Harmer's map. It emerged that Harmer had compiled it in old age, having originally learned glacial geology in the later 19th century. Examination of both his text and the distribution map show that it drew upon a limited number of (unstated) sources that did not include the schedules of erratics drawn up by either the BAAS or the local glacialists. Consequently, drawing on all the printed sources by then known to me, I compiled my own map of distributed Lake District greenstone (and some other) erratics, to accompany my essay on Cumbrian axes in 1989 (Briggs 1989; Fig. 3).

A similar movement of boulder observers was initiated in France through the Mineralogical Section of the French Academy of Sciences in 1878. In common with the British project, one of its main objectives was to preserve boulders as well as identify them (Daubrée 1878), but after some initial catalogues were made and maps had been drafted, the project seems to have fizzled out with publication of only a few results (cf. Anon 1868). Nowadays even such records as were printed seem to be neglected by both geomorphologists and archaeologists. This is a particularly worrying omission in the context of Neolithic stone procurement, as the Alpine glaciation must have had a fundamental impact upon the natural distribution of pebble jadeite, cherts, flints and related types of rock (cf. the distributions of chert and flint artefacts in Binsteiner and Ruprechtsberger 2006).

An important outcome of boulder watching was the collection and deposition of unusual, far-carried rocks into private and public parks. A number are preserved in St Mary's Abbey Gardens, outside the Yorkshire Museum at York (where the 2007 IPG Conference was held). Examples still to be seen include Shap Granite and greenstone from the Lake District (Fig. 4). These were deposited in the gardens, having been brought from different parts of the city during 19th-century excavations for building developments. One of these greenstone boulders alone would furnish a dozen or more Neolithic stone axes similar to those that were flaked from Borrowdale volcanics on the slopes of Langdale (in the Lake District). Others can be seen on village greens in the Vale of York and many more are known from much further afield, distributed throughout Britain. The garden of Wightwick Manor, a National Trust property outside Wolverhampton, possesses an interesting group of granite-like boulders found locally in the 19th century, which it is suggested came from Scotland and the Lake District (Fig. 5).

But to return to the 19th-century observers. Once lists of provenanced boulders had been compiled, distribution patterns were committed to maps, indicating the (often multi-) directional dispersal of particular rock varieties. The most spectacular colourful stones were the easiest to track. Shap granite overrode the Pennines and poured south along the east of the Pennines (Fig. 6); plucked from an outcropping island in West Scotland, fragments of Ailsa Craig microgranite peppered the coasts of the Irish Sea; Welsh rocks were noted in the Midlands; Borrowdale volcanics and Eskdale granite (Fig. 7) were found to be common throughout much of northern Britain, and the Lake District itself was seen to have been invaded by ice from Scotland (Fig. 8). Of remoter origin, Scandinavian stones were recognised the length of Britain's eastern seaboard, producing boulders that were often visually spectacular like Lavrikites, rhomb porphyries and greenstones. Until these erratics have been subjected to the same detailed geochemical and petrographic examination as the stone axes, the degree to which they may have been used in prehistoric or historic times will remain a matter of speculation.

It is important to emphasise at this point that for almost two centuries now, the identifications of all these boulders have been made from visual inspection in hand specimen and there are few, if any comprehensive reference collections of erratics or pebbles found naturally in the soil available for comparative purposes. It is a matter of curiosity that some confident identifications (like the Borrowdale volcanics recorded from the Yorkshire coast after 1870), were being made before the petrology of Ordovician vulcanicity in Borrowdale itself was understood: before a serious understanding of petrography as we now know it had developed, and long before the Nichols microscope was routinely used in the laboratory. Few 19th-century boulder-watching enthusiasts ever had access to detailed mineral examinations or petrographic analyses for their discoveries.

Their research was not undertaken in vain, however. As the Geological Survey's investigators slowly covered Britain and Ireland, they were able to make use of and add to the boulder-watchers' observations. Local information on glacial deposits was accordingly incorporated into the texts of official district and regional geological memoirs. Studies of erratics also appeared as articles in local and national geological journals.

Unfortunately, as confidence grew in the belief that sufficient was known about glacial direction and process, examining erratics eventually became unfashionable. It was felt that a limited amount was to be deduced from looking at boulders and much more would probably be learnt from examining stratified sediments and their clasts.

By the 1970s, few scholars were creating distribution maps and hardly anyone was collecting information on erratics. In 1949 P.A. Sabine had examined a group of erratics in the Nene Valley, Northamptonshire (Fig. 9). His source map showed how a half-dozen different rock-types reached Northamptonshire variously from the Lake District, North Wales, parts of Midland England and Cornwall. This is a particularly useful study, demonstrating how south-western stone first came into the Midlands as pebbles during the Triassic, long before the Quaternary Ice Ages (Wills 1948). Later geological events, particularly during the Quaternary, then re-cycled these pebbles both fluvially and glacially, redistributing them to the north, east and south. When I first encountered Sabine's paper, I wondered why it was never mentioned by implement petrographers, because it seemed to offer important clues about how the materials for Neolithic polished stone axes really travelled.

Today it is fascinating to discover that members of the Hull Geological Society have resuscitated the work begun by their predecessors well over a century ago. All kinds of Scandinavian erratic are nowadays to be seen on their website; cf. www.hull.ac.uk/php/chsmjh/erratics.htm] and indeed on the websites of others who are collecting these data up and down Britain. To celebrate the millennium, the Lincolnshire Wildlife Trust produced a pamphlet instigating a new erratics survey in collaboration with the local RIGS (Regionally Important Geological Sites) group. Its outcome is unknown at the time of writing,. The welcome establishment of an online database of the erratics collection at Norwich Castle Museum is a more recent departure (Larkin and Hoare 2009). These and similar resources elsewhere offer a useful starting point for future petrographic sampling programmes

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