STRACHEY, JOHN

(b. Sutton Court, Chew Magna, Somerset, England, 10 May 1671; d. Greenwich, England, 11 June 1743)

Geology.

Strachey was the only son of John and Jane Strachey. He inherited his father’s estate when three years old. Little is known about his education and early life. On 26 November 1686, he matriculated at Trinity College, Oxford, but left to study law at Middle Temple, London, in 1687. In 1692 Strachey married Elizabeth Elletson, who bore him eighteen children, and, two years after her death in 1722, Christina Stavely, by whom he had a son. He resided mainly at Sutton Court but spent the latter part of his life in Edinburgh. In 1719 he was elected fellow of the Royal Society.

In the early eighteenth century there were several coal mines near Sutton Court; and it was probably Strachey’s interest in them that led him to study geology, for he published two geological papers and a pamphlet, all relative to occurrences of coal in Somerset and elsewhere. In the first two he included diagrams showing a cross section several miles long of the strata in the region of Sutton Court, based on an intimate knowledge of the coal workings and an examination of rock outcrops in the surrounding countryside. They showed nearly horizontal Jurassic, Triassic, and (in his 1725 paper) Cretaceous strata resting on steeply inclined Coal Measures (Pennsylvanian). This was the first clear demonstration by a British author of an angular unconformity. Within the Coal Measures he recorded seven named seams, one of which was characterized by the fossil shells and plants occurring above it, a very early use of fossils to identify a specific horizon. The diagram also showed the effect of a fault on the continuity of the coal seams.

In his 1727 pamphlet Strachey restated his earlier observations and added details of the strata in other coalfields in England and Scotland, based partly on his own observations. He described the lithological characteristics of the coal seams and associated sediments, but seems to have had little idea how they were formed and hence did not realize the significance of the unconformity he recorded. Strachey recognized the importance of dip and strike, noting that across a broad belt of England, strata in general dip to the east and southeast. To account for it he accepted the suggestion already made by some British authors that all rock formations continue downward to the center of the earth, as a result of the west-to-east rotation of the earth acting on strata that originally were soft and unconsolidated.

Strachey left a number of unpublished manuscripts, one of which, since published, “Of Stones,” is of considerable geological interest as a record of early eighteenth-century mining and quarrying operations in England. He also published a map of Somerset showing the sites of coal and metalliferous mines.

Strachey’s work is of value as an early attempt to establish a stratigraphical succession, but the importance of the unconformity he recorded was not realized until much later.

BIBLIOGRAPHY

I. Original Works. Strachey’s writings include “A Curious Description of the Strata Observ’d in the Coal-Mines of Mendip in Somersetshire,” in Philosophical Transactions of the Royal Society, 30 (1719), 968–973; “An Account of the Strata in Coal-Mines, &c.,” ibid., 33 (1725), 395–398; Observations on the Different Strata of Earths, and Minerals. More Particularly of Such as Are Found in the Coal-Mines of Great Britain (London, 1727); Somersetshire Survey’d and Protracted (London, 1736), a map of Somerset, on the scale of about 1/2 inch to the mile; and “Of Stones” (ca. 1736), from the MS of John Strachey’s proposed “Somersetshire Illustrated,” annotated by R. D. Webby, in Proceedings of the Bristol Naturalists’ Society, 31 , no. 3 (1967), 311–330. Strachey’s MSS are preserved in the Somerset Record Office, Taunton, England.

II. Secondary Literature. See J. G. C. M. Fuller, “The Industrial Basis of Stratigraphy: John Strachey, 1671–1743, and William Smith, 1769–1839,” in Bulletin of the American Association of Petroleum Geologists, 53 , no. 11 (1969), 2256–2273; and J. D. Webby, “Some Early Ideas Attributing Easterly Dipping Strata to the Rotation of the Earth,” in Proceedings of the Geologists’ Association, 80 , pt. 1 (1969), 91–97.

V. A. Eyles