On the meaning of the term 'Silurian system' as adopted by geologists in various countries during the last ten years / by Sir Roderick Impey Murchison.

  • Murchison, Roderick Impey, 1792-1871.
Date:
1852
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Licence: Public Domain Mark

Credit: On the meaning of the term 'Silurian system' as adopted by geologists in various countries during the last ten years / by Sir Roderick Impey Murchison. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    rock with the Llandeilo flags, as has since been done by the Govern- ment Surveyors ; nor does it ever appear to have occurred to Professor Sedgwick that these were beds of about the same age as those which we had seen together on the east flank of the Berwyns, on the banks of the Twrch, where they were recognized by me as “Llandeilo Flags.” But having afterwards ascertained that several species of Ortliidse which occur in the Bala rock were common both to the Caradoc and Llandeilo formations, I specially stated, four years after- wards, in publishing the ‘Silurian System’ (1838), “As these shells abound also in the Lower Silurian rocks, it would seem that as yet no defined line of zoological division can be drawn between the Lower Silurian and Upper Cambrian groups, and that, as our knowledge extends, we may probably fix the lowest limit of the Silurian System beneath the line of demarcation which has for the present been assumed*.” In reference to the argument about a “ base-line,” as employed by Professor Sedgwick, I must state that in the whole ‘Silurian System’ the term “ base-line” is never once applied to these rocks. I had quite labour enough within my own region, without being made re- sponsible for the accuracy of the western boundary of my original map of 1830, that separated Siluria from Cambria; but which ten years ago I abrogated, as being wholly inaccurate. That line was, I maintain, a boundary merely between one region whose contents had been worked out and published, and another whose fossil contents were unpublished and therefore unknown. The simple question, then, which every practical geologist has long ago answered in the negative, is this, Was the Cambrian system ever so defined, that a competent observer going into an uninvestigated country could determine whether it existed there ? That it was never so characterized is demonstrated by the successive publications of Professor Sedgwick himself, to say nothing of the inferences of every one of our contemporaries who have examined countries at home or abroad in which such rocks occur. For wherever well-known Lower Silurian fossils occurred in such countries, the tracts so typified have necessarily been called Silurian. (1836-38.) I have already stated, that during the establishment of the Silurian System and up to the period when it was so named, Professor Sedgwick published nothing on the subject; and, although he refers to a Cambridge Syllabus of Lectures drawn up in 1836, and issued early in 1837, wherein he uses the word “Cambrian” (I have referred above also to the communication made at the Dublin Meet- ing of the British Association), it is only in 1838 that we meet with the first published abstract of a real memoir, his “ Synopsis of the English Series of Stratified Rocks inferior to the Old Red Sand- stone”')' ; followed in 1841 by the “ Supplement to a Synopsis of the English Series of Stratified Rocks inferior to the Old Red Sand- stone:);.” For the indistinctness of the author’s views on those oc- casions respecting the fossil contents of his Cambrian rocks (two or * 1 Silurian System,’ p. 308. f Proceed. Geol. Soc. vol. ii. p. 675 el seg.
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