First sketch of a new geological map of Scotland with explanatory notes
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An Address Delivered at the Anniversary Meeting of the Geological Society of London on the 17th February, 1832.
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On the Geological Structure of the Central and Southern Regions of Russia in Europe, and the Ural Mountains
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Sir Roderick Impey Murchison was a Scottish geologist who first described and investigated the Silurian system.
Background
Roderick was born at Tarradale, Rosshire, Scotland, United Kingdom on February 19, 1792. Murchison was born into a long-established family of Highland landowners. His father, Kenneth Murchison, died when the boy was only four; and after his childhood he never lived in Scotland.
Education
He was educated at the military college at Great Marlow and in 1808 saw active service briefly in the Peninsular War.
A chance acquaintance with Humphry Davy turned his attention toward science, however, and in 1824 he settled in London and attended lectures at the Royal Institution.
Career
In 1828 he accompanied Charles Lyell through the celebrated volcanic districts of the Massif Central into northern Italy, and their joint papers suggest that Murchison was at this time much influenced by Lyell’s theoretical views.
It was widely doubted whether the method of correlation by fossils would even be applicable to these ancient Transition strata, yet in them—if anywhere—lay the possibility of finding evidence for the origin of life itself.
Acting on a hint of Buckland’s, Murchison was fortunate to find in the Welsh borderland an area in which there was a conformable sequence downward from the Old Red Sandstone into Transition strata with abundant fossils.
It thus seemed to Murchison to mark a major period in the progressive history of life on earth.
Even before he had completed his great monographic account The Silurian System (1839), its validity had been rapidly recognized by geologists in many other parts of the world.
If the Silurian period had truly predated the establishment of terrestrial vegetation, the recognition of Silurian fossils in any part of the world would reliably indicate a base line beneath which it was pointless to search for coal: this would save much useless expenditure and also help to assess more accurately the possible reserves of undiscovered coal.
A report by Henry de la Beche of coal plants in the “grauwacke”of Devonshire (1834) therefore seemed to Murchison to be a very serious anomaly, and he devoted several years to an attempt to explain it away.
He and Sedgwick discovered first that the fossil plants were in fact in strata of Coal Measure age overlying the true “grauwacke”; and later, in 1839, following a suggestion of William Lonsdale’s, they concluded that even these older strata were not pre-Silurian, as they had originally thought, but were the lateral equivalents of the Old Red Sandstone.
This definition of a Devonian system was at first criticized as being based purely on paleontological criteria and not on any plain evidence of superposition; but Murchison and Sedgwick soon showed that the distinctive Devonian invertebrate fauna occurred in Westphalia in the expected position immediately below the Carboniferous strata.
The following year (1840) Murchison resolved the matter by discovering in European Russia a sequence of undisturbed strata in which the Devonian was clearly underlain by Silurian and overlain by Carboniferous, and in which Devonian invertebrates were interbedded with Old Red Sandstone fish.
At the same time it showed him how undisturbed and unaltered sediments could change their appearance radically when traced laterally into a region of mountain-building, and this convinced him of the validity of Lyell’s hypothesis of meta- morphism.
It was now shown much more seriously in his controversy with Sedgwick over the base of the Silurian.
In the same year that Murchison had first investigated the Transition strata, Sedgwick had begun to unravel still older strata in Wales; and when Murchison first established the Silurian, Sedgwick had suggested the name Cambrian system (after the Latin name for Wales) for the older rocks.
During their only joint fieldwork in Wales (in 1834) Murchison had assured Sedgwick that the latter’s Upper Cambrian lay below his own Lower Silurian strata, although, as expected, there was a faunal gradation between the two.
But when Murchison later realized that the fossils of the Upper Cambrian Bala series were indistinguishable from his own Lower Silurian Caradoc series, he boldly proclaimed their identity and annexed the Upper Cambrian into his Silurian system. Sedgwick protested that the Cambrian had been clearly defined by reference to an undisputed succession of strata in northern Wales and that it was wrong to alter the meaning of the term just because its upper part contained Silurian fossils.
But Murchison continued to annex more and more of the Cambrian into his Lower Silurian, until the two terms were virtually synonymous.
Sedgwick claimed that this unjustified annexation was designed to cover two major mistakes of Murchison’s.
Thus, when Murchison wrote his Geology of Russia (1845), he asserted that the “unequivocal base—line of palaeozoic existence” was to be seen in the Lower Silurian strata, within which there was a “gradual decrement and disappearance of fossils” toward the base.
Furthermore, in Scandinavia (where he had traveled in 1844) these strata were immediately underlain by “Azoic” crystalline schists, in which Murchison believed that it was “hopeless to expect” to find fossils.
This was not because they had been metamorphosed (although he agreed that they resembled the metamorphic rocks of later periods) but because they had been formed under conditions too hot to support life.
He therefore argued, against Lyell, that geology provided “undeniable proofs of a beginning” to life on earth.
Thus when Joachim Barrande first described a distinctive “primordial” fauna (the Cambrian of modern geology) below the previously known Lower Silurian faunas, Murchison did not allow it as a possible paleontological basis for Sedgwick’s Cambrian but incorporated it too into his Silurian. In 1846 Murchison was knighted and served as president of the British Association for the Advancement of Science; and in 1849 his work was recognized by the award of the Royal Society’s Copley Medal.
He later published an updated and more popular version of his work as Siluria (1854), expressly in order to deliver a “knock-down blow” (the aggressive metaphor is characteristic) to those, like Lyell, who still denied the reality of organic progres- sion.
He opposed the glacial theory of Louis Agassiz and continued to assert that icebergs alone had been responsible for the transport of erratic blocks (“drift”) long after most other geologists had accepted at least a modified glacialism: under his influence the Geological Survey’s maps long continued to use the term “drift” for glacial and postglacial deposits.
Murchison’s last major fieldwork, in 1858–1860, was devoted to arguing that the Moine schists of the northwestern Highlands were Silurian sediments, although he had always favored relatively catastrophist interpretations of mountain tectonics and had been convinced a decade earlier of the reality of large-scale thrusting in the Alps.
He was totally opposed to Darwin’s evolutionary theory. Murchison retired temporarily from the council of the Geological Society in 1863 and was therefore eligible to be awarded the Wollaston Medal the following year.
He was created a baronet in 1866.
He had earlier been one of the founders of the Royal Geographical Society and was for many years its president.
The Murchison Falls of the Nile in Uganda are named after him.