Siluria : a history of the oldest rocks in the British Isles and other countries with sketches of the origin and distribution of native gold, the general succession of geological formations, and changes of the earth's surface / by Sir Roderick Impey Murchison.

Roderick Murchison, 1st Baronet

Date:: 1867

Credit: Siluria : a history of the oldest rocks in the British Isles and other countries with sketches of the origin and distribution of native gold, the general succession of geological formations, and changes of the earth's surface / by Sir Roderick Impey Murchison. Source: Wellcome Collection.

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$Eeverting now to the Silurian region proper, in which those researches began which enabled me to prepare the ‘ Silurian System,’ I take leave of the Laurentian rocks with the expression of my belief that they have no existence in England and Wales, nor, as far as I know, in Ireland*. The most zealous researches of collectors and palaiontologists during the last quarter of a century, though pertinaciously directed to tliis point, have failed in detecting any other traces of former life in the Cambrian rocks y than the few relics which will presently be described—albeit in a large portion of their range the Cambrian strata of the Longmynd, having an estimated thickness of 26,000 feet, are very slightly altered. No sooner, j however, do we examine the deposits formed subsequently than we meet thenceforward with a never-failing storehouse of organic remains. In the lithograph given in the Frontispiece, repeated from the former edition, there is an attempt to represent, by colour and indications of stra- tification, the succession of the most ancient rocks as seen in looking west- ward from Inchnadamff on Loch Assynt in Sutherland. Thus the low distant hills forming the sea-coast consist of that fundamental or Laurentian gneiss {a) which is older than any rock in England and Wales. Next, the lofty mountain of Queenaig, composed of horizontal, chocolate-coloured, hard sandstone and conglomerate (6), is of the same age as the Cambrian rocks of the Longmynd in Shro])shire, and Harlech in Wales, which, as wiU pre- sently he shown, lie beneath the whole of the Silurian strata of Wales and England. The overlying sloping masses descending into the foreground are quartzites or altered sandstones (c^ and c'*), with included crystalline limestones (r); and these (when they range into Durness) contain about twenty species of Lower Silurian fossils f. After a short sketch of the earliest or Cambrian zone of sediments of the Silurian region, fall descriptions will he given of the Lower and Upper Silurian rocks. Other chapters will treat of the strata (now termed Llandovery rocks) which unite the two groups, and of the up- per members of this great natural series. Whilst so separated for purposes of classification, it will, however, he clearly shown that, i through their organic remains, those deposits comprehend but one great system of life. Condensed accounts will then follow of the overlying or * Inasmuch as the EozoonCanaclense frequently tion of the belief that a marine creature of that occurs in S(‘rpentinou8 limestone, it was at one time class in ay have lived on from the Laurentian to ^ supposed that it had been discovered in the f^'reen the Silurian era. Thus some of the Foraminifera marble of the Connemara Mountains in Ireland, represented bv siliceous cast s in the Lower Silurian In a future paj'c it will be shown that this Irish ^^reen sand of Ilussia (as will be noticed in tht; rock is of Lower Silurian age. Now, without seqmd) are probably identical with existing entering into the controversy respecting the true species ; and Nodosarinm undistinguishuble from character of the Eozoon, I may state tliat much living forma are found in the Permian limestones, ability was dispWed by Dr. liowney and Profes- IMany others also have lived on from the Seeon- ‘ sor W. King, of Galway, in their recent effort to dar} periods; and the same Globigerina that con- show that the forms of Eozoon which they exa- atitutes great masses of the Clialk now coats the mined were purely referable to chemical and bed of the Atlantic and other oceans, mineral conditions. On this point I will only say t These fossils, discovered by Mr. C. Pi'ach, are that, believing, as I do, the Eozoon to be a Fora- described in the Ninth Chapter, minifer, I can see no valid objection to the adop-$