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| Keywords: The Quarterly journal of the Geological Society of London (12645076783).jpg 1848 NICOL ON RECENT FORMATIONS NEAR EDINBURGH 21 <br> tons in weight and generally derived from trap sandstone or lime- <br> stone rocks like those composing the coal-field on which it rests <br> Fig 2 <br> Some of these boulders however consist of granite mica-slate or <br> other primary strata and must consequently have been carried a <br> greater distance as none of these rocks are found nearer than from <br> forty-five to fifty miles and granite in any quantity only at seventy <br> miles' distance These boulders are generally rounded and water- <br> worn but some on the contrary are angular They are found in <br> every part of the mass of blue clay but as it seemed to me in more <br> abundance in certain portions and apparently arranged in horizontal <br> lines <br> These facts appear to prove that the deposition of this boulder <br> clay or till was gradual ” the effect of long-continued and variable <br> agents ; and not of a sudden rush of water or debacle as has been <br> imagined The whole phsenomena seem more consistent with the <br> supposition that the clay was formed by the continuous action of the <br> sea on the various strata of the subjacent coal-field than with any <br> other theory The blue clay forming the great bulk of the till may <br> be regarded as merely the decomposed shales of the coal formation <br> and the sands as comminuted sandstones even the relative position <br> of the deposits with the blue clay below and a browner and more sandy <br> clay resting upon it as seen in the sections favours this opinion The <br> soft shales when exposed to the action of the waves would be wasted <br> away before the harder sandstones and trap rocks and the deposit <br> formed from their destruction would consequently occupy a lower <br> position The boulders may have been brought to the place where <br> we now find them by ice or entangled in the roots of floating trees <br> or in any other mode now in action for the transport of rock masses <br> Though mixed up irregularly with the mass of clay it is by no means <br> necessary that they should have been always transported along with it <br> or by the same agent Were a number of boulders at the present <br> day dropped on a mass of soft semifluid clay at the bottom of the sea <br> they would not remain on the surface but sink in it to various depths <br> and thus appear to have been deposited by the same agents when in <br> reality they were deposited by wholly different causes Neither does <br> the apparent want of stratification in the clay prove it to have been 35268655 109512 51125 Page 21 Text v 5 http //www biodiversitylibrary org/page/35268655 1849 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 5 1849 Geology Periodicals Smithsonian Libraries bhl page 35268655 dc identifier http //biodiversitylibrary org/page/35268655 smithsonian libraries Information field Flickr posted date ISOdate 2014-02-20 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12645076783 2015-08-27 10 55 09 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1849 Photos uploaded from Flickr by Fæ using a script | ||||
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