James Hutton : biography
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At Glen Tilt in the Cairngorm mountains in the Scottish Highlands in 1785, Hutton found granite penetrating metamorphic schists, in a way which indicated that the granite had been molten at the time. This showed to him that granite formed from cooling of molten rock, not precipitation out of water as others at the time believed, and that the granite must be younger than the schists.
He went on to find a similar penetration of volcanic rock through sedimentary rock near the centre of Edinburgh, at Salisbury Crags, adjoining Arthur’s Seat: this is now known as Hutton’s Section. He found other examples in Galloway in 1786, and on the Isle of Arran in 1787.
Hutton Unconformity at [[Jedburgh. Photograph (2003) below Clerk of Eldin illustration (1787).]] The existence of angular unconformities had been noted by Nicolas Steno and by French geologists including Horace-Bénédict de Saussure, who interpreted them in terms of Neptunism as "primary formations". Hutton wanted to examine such formations himself to see “particular marks” of the relationship between the rock layers. On the 1787 trip to the Isle of Arran he found his first example of Hutton’s Unconformity to the north of Newton Point near Lochranza, but the limited view meant that the condition of the underlying strata was not clear enough for him, and he incorrectly thought that the strata were conformable at a depth below the exposed outcrop.
Later in 1787 Hutton noted what is now known as the Hutton Unconformity at Inchbonny, Jedburgh, in layers of sedimentary rock. As shown in the illustrations to the right, layers of greywacke in the lower layers of the cliff face are tilted almost vertically, and above an intervening layer of conglomerate lie horizontal layers of Old Red Sandstone. He later wrote of how he "rejoiced at my good fortune in stumbling upon an object so interesting in the natural history of the earth, and which I had been long looking for in vain." That year, he found the same sequence in Teviotdale.
An eroded outcrop at [[Siccar Point showing sloping red sandstone above vertical greywacke was sketched by Sir James Hall in 1788.]] In the Spring of 1788 he set off with John Playfair to the Berwickshire coast and found more examples of this sequence in the valleys of the Tour and Pease Burns near Cockburnspath. They then took a boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of Dunglass. They found the sequence in the cliff below St. Helens, then just to the east at Siccar Point found what Hutton called "a beautiful picture of this junction washed bare by the sea". Playfair later commented about the experience, "the mind seemed to grow giddy by looking so far into the abyss of time". Continuing along the coast, they made more discoveries including sections of the vertical beds showing strong ripple marks which gave Hutton "great satisfaction" as a confirmation of his supposition that these beds had been laid horizontally in water. He also found conglomerate at altitudes that demonstrated the extent of erosion of the strata, and said of this that "we never should have dreamed of meeting with what we now perceived”.
Hutton reasoned that there must have been innumerable cycles, each involving deposition on the seabed, uplift with tilting and erosion then undersea again for further layers to be deposited. On the belief that this was due to the same geological forces operating in the past as the very slow geological forces seen operating at the present day, the thicknesses of exposed rock layers implied to him enormous stretches of time.
- 1785. Abstract of a dissertation read in the Royal Society of Edinburgh, upon the seventh of March, and fourth of April, MDCCLXXXV, Concerning the System of the Earth, Its Duration, and Stability. Edinburgh. 30pp.
- 1788. The theory of rain. Transactions of the Royal Society of Edinburgh, vol. 1, Part 2, pp. 41–86.
- 1788. Theory of the Earth; or an investigation of the laws observable in the composition, dissolution, and restoration of land upon the Globe. Transactions of the Royal Society of Edinburgh, vol. 1, Part 2, pp. 209–304.
- 1792. Dissertations on different subjects in natural philosophy. Edinburgh & London: Strahan & Cadell.
- 1794. Observations on granite. Transactions of the Royal Society of Edinburgh, vol. 3, pp. 77–81.
- 1794. A dissertation upon the philosophy of light, heat, and fire. Edinburgh: Cadell, Junior, Davies.
- 1794. An investigation of the principles of knowledge and of the progress of reason, from sense to science and philosophy. Edinburgh: Strahan & Cadell.
- 1795. Theory of the Earth; with proofs and illustrations. Edinburgh: Creech. 2 vols.
- 1797. Elements of Agriculture. Unpublished manuscript.