In 1830 De la Beche began a more systematic geological examination of south Devonshire utilising the Ordnance one-inch map as a base.
His detailed notes, together with sections, may be found in a notebook preserved in the Library of the British Geological Survey (GSM 1/123).
The region covered by these recorded observations is confined largely to Ordnance sheets 22 and 23 (see Figure 16).
The area previously mapped around Tor and Babbacombe bays was now revisited and fleshed out in greater detail.
This was for De la Beche a recreational activity that depended on his receiving a regular income from his plantation in Jamaica.
But by 1831 this was in jeopardy. For some years the price of sugar had been declining steadily, due in large part to overproduction.
This excess was most notable in Cuba, where sugar production more than doubled in the years between 1829 and 1836. In 1831 the average price of raw sugar fell to a lower level than at any time previously. Many plantations in the English colonies, including De la Beche’s,
were by this time heavily mortgaged, causing yet more distress to the
owners (Deerr 1949–50).
It remains unclear whether, as De la Beche was to claim, he began the geological mapping of whole Ordnance map sheets purely for his own recreation, or whether this was done from the start with an eye to selling the idea to the Ordnance Survey.
He was in regular correspondence with Élie de Beaumont, who at this time was engaged in mapping the geology of France at government expense.
Thus the French geologist wrote to him in May 1830 with the news that he was then engraving the map of France (Sharpe & McCartney 1998, item 492).
Whatever his reasons, the year 1831 saw De la Beche pressing ahead with his fieldwork in south Devonshire, driven by a sense of urgency that kept him there through the rainy months of late autumn (Figure 11).
On 28 March 1832, De la Beche addressed a letter to the Master General of the Board of Ordnance with a proposal ‘for supplying the data for colouring Geologically eight Sheets of the Ordnance Map of England, viz. Nos. 20, 21, 22, 23, 24, 25, 26 & 27, comprising Devonshire, with parts of Cornwall, Somerset, & Dorset’ (GSM 1/68, 44-8).
De la Beche took care to address his proposal from the offices of the Geological Society, of which he was then Secretary, thereby ensuring that it would receive serious consideration.
The proposal ran as follows:
‘Having applied myself to the Study of Geology for many years and having directed much of my attention to the Geological relations of this my native country … and being convinced of the great practical utility of what I am about to propose, I offer no apology for intruding myself on the notice of your Honble Board with a view to obtain the completion of an undertaking which has for some time past occupied much of my time and attention; one that I had set out with the intention of accomplishing at my own proper cost, but in which I am defeated by the failure of certain funds I had intended to apply to that purpose.
I am induced therefore to offer to your Honble Board the fruits of my labours at a price that I am well assured will be considered very moderate knowing as I do that it will be much below the sum they will have cost me when completed. ... For the sum of £300, I undertake, within two years from the present time, accurately to determine for the use of the Ordnance solely the Geological structure of the district comprised within the eight sheets specified above and to lay down the detail accurately to scale and properly coloured upon each of those sheets, in so clear and intelligible a manner as to admit of its being readily transferred upon the Ordnance Copper Plates.
I will also attach to the margin of each sheet an index scale of colours descriptive of the rocks and beds comprised within it.’
De la Beche followed this with a detailed cost benefit analysis.
Thus, for an Ordnance sheet currently retailing at 12 shillings, the addition of geological data would increase the selling price by a further two shillings.
He had little doubt that the Ordnance would fully recover its costs on the sale of these maps, and saw every prospect that the work would confer ‘a great benefit on a Science that is every day increasing in interest and importance’, while the resulting maps ‘would be of great practical utility to the Agriculturalist, the Miner, and those concerned in projecting and improving the Roads, Canals, and such other public works, undertaken for the benefit and improvement of the Country.’
De la Beche had already completed the geological mapping of Ordnance sheet 22 (Figure 12) at the time of writing his proposal. It was probably this sheet also that he despatched to Élie de Beaumont, who thanked him in a letter dated 8 April 1832, expressing the hope that this initiative would lead to the completion of the remaining sheets (Sharpe & McCartney 1998, item 497).
Clearly, De la Beche must have been confident of a successful outcome.
The Board forwarded the proposal to Lt-Col. Thomas Colby, Superintendent of the Ordnance Survey (Figure 13), for his opinion.
De la Beche’s proposal fitted well with Colby’s ambition to increase the utility of Ordnance maps by the addition of geological information as was already being tried, albeit with limited success, in Ireland.
Colby was also cautiously encouraging his English surveyors to include geological observations on their maps, so long as it did not impede the progress of the topographical survey (Harley 1971; Murchison 1833, 446-7).
De la Beche had even issued a ‘Table of Letters and Colors by which the Rocks and Strata of most ordinary occurrence will be expressed’ (Colby 1830).
It therefore comes as no surprise that in his reply to the Board, dated 9 April, Colby acceded to the proposal, though on certain conditions: firstly, that the index of colours to be used should be referred to the Council of the Geological Society for their decision; secondly, that De la Beche ‘shall undertake, at his own cost and risk to publish all these indexes of Colors, Geological Sections, Memoirs, and other matters which may be necessary to illustrate the use of the Map where Geologically colored.’
The sum of £300 would be paid in eight equal instalments of £37 10s upon delivery of a sheet geologically coloured for engraving (GSM 1/68, 52-3).
On 2 May De la Beche was formally invited to accept the Board’s offer subject to the above conditions. In his reply to Colby he quibbled only at the necessity of referring his index of colours to the Council of the Geological Society, warning that a speedy decision would be unlikely and could only delay matters.
Some formal consultation with the Society did however take place, and De la Beche discussed the matter privately with G B Greenough (a close friend and future ally) who was then preparing a second edition of his Geological Map of England & Wales.
The two of them agreed a provisional scheme of colours, which De la Beche then applied to the finished sheet 22.
This sheet he delivered to the Ordnance Map Office at the Tower of London on 9 May, the same day on which he formally accepted the Board’s offer (GSM 1/68, 56-65, 83). Although impatient to begin fieldwork, he delayed his departure in order to attend a meeting of Council on 16 May, at which an agreement by committee was reached on the scheme of colours, as appears from a manuscript table of 16 colours preserved in the Library of the British Geological Survey (GSM 1/85; Woodward 1908).
These colours were chosen to match the prevalent tints of the rocks themselves, a practice recommended by Abraham Werner of the Freiberg Mining Academy in Saxony, and advocated in Britain by Robert Jameson (Jameson 1811). William Smith had likewise applied the same general principal in colouring his maps (Smith 1815).
Further deliberation on the scheme of colours appears however to have taken place during the winter of 1832, evidently because De la Beche discovered a need for additional colours during the course of mapping.
The Council sought the advice of the sculptor and painter, Francis (later Sir Francis) Chantrey, a member of the Society well regarded for his experience in the applied arts (Cook 1987).
The subsequent colour indexes issued by De la Beche may therefore owe something both to the Wernerian principal and to Chantrey’s design sense, although the scheme would evolve in the years to come as more geological formations were identified and additional colours and patterns needed (Figure 14).
No official correspondence survives from the two-and-a-half-year period during which De la Beche worked on the Devonshire sheets.
However, in his February 1834 presidential address to the Geological Society, Greenough was able to report that ‘Mr. De la Beche, one of our Vice-Presidents, acting under the direction of the Board of Ordnance, has produced a geological map of the county of Devon, which, for extent and minuteness of information and beauty of execution, has a very high claim to regard’ (Greenough 1834, 51).
In his next address the following year we learn that ‘The researches of your Vice-President in the counties of Devon and Somerset have been carried on this year [1834–35] with increased energy.
Of the eight sheets of the Ordnance Map upon which he has been engaged, four were published last spring [probably sheets 22–25], three others are complete, the eighth is nearly complete, and an explanatory memoir with sheets of sections applying to the whole are to be published before our next anniversary.’
Greenough had been carefully primed by De la Beche, and he ended with the plea: ‘Let us hope that this work so admirably begun may not be suffered to terminate here’ (Greenough 1835, 154; Rudwick 1985, 123–4).
Bate, D G. 2010 Sir Henry Thomas De la Beche and the founding of the British Geological Survey. Mercian Geologist, 17 (3). 149–165.