MAKE A MEME View Large Image The Quarterly journal of the Geological Society of London (13205993984).jpg 92 PROCEEDINGS OF T« GEOLOGICAL SOCIETY DeC 2 <br> suggestion as the lines appear to correspond to portions of curves <br> having a common axis But as each of the ...
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Keywords: The Quarterly journal of the Geological Society of London (13205993984).jpg 92 PROCEEDINGS OF T« GEOLOGICAL SOCIETY DeC 2 <br> suggestion as the lines appear to correspond to portions of curves <br> having a common axis But as each of the planes runs in the same <br> position for a great distance if the curves were completed they would <br> represent a series of semicylinders turned over a common axis <br> The arrangement of the planes of cleavage on so symmetrical a <br> plan is in itself deserving of attention ; but when their direction is <br> compared with the position of the beds over the same area we find <br> coincidences too remarkable to be due to accident and which lead <br> to considerations of great importance connected with the elevation <br> and disturbance of portions of the crust of the globe The remarks <br> which follow will be made intelligible by reference to my map of part <br> of North Walesf and to the sections figs 17 and 18 in which the <br> ' Figs 17 and 18 <br> 1 Snow don 2 Rhaiadr Cwm 3 Bala <br> minor irregularities are omitted and only the main features preserved <br> to prevent the attention from being distracted by minutiae all subor- <br> dinate to the larger phsenomena Fig 17 represents the position <br> of the beds along a section of the country from the W side of Snow- <br> don to the slate bed E of Bala fig 18 the dip of the cleavage planes <br> along the same line of section <br> At Rhaiadr Cwm which is on the axis of the elevation of all the <br> planes of cleavage of the area there is an anticlinal axis of the stra- <br> tification along which the oldest rocks of this part of North Wales <br> are brought to the surface in a low flat arch J which forms but a slight <br> feature in the country ; this now proves of great significance as it <br> must be considered the true axis of elevation of the whole area both <br> of the cleavage planes and the stratification We cannot trace this <br> axis for more than a few miles either to the N E or the S W as in <br> both directions it is entangled in great masses of erupted igneous <br> rocks In Professor Sedgwick's map of North Wales § the line laid <br> down as the great Merioneth anticlinal is parallel to the axis at <br> Rhaiadr Cwm but is drawn five miles to the S E of it <br> On both sides of this central axis there is a relation between the <br> inclination of the cleavage planes and the elevation of the strata <br> where the dip of the cleavage is at the lowest angle the elevation of <br> the beds is most moderate and they are but slightly disturbed ; where <br> the cleavage dips at a higher angle the beds are more elevated and <br> disturbed and their dip occasionally reversed ; and near the boundaries <br> ' ¢ Although in theory we ought to regard the cleavage as arranged in curves I <br> have continued to use the term cleavage jy/anes to which we are accustomed from <br> dislike to introducing a new term and because to our senses they appear planes and <br> not curves <br> t Quarterly Journal of Geological Society vol ii pi 12 xltefs'i airiT <br> X Ibid vol ii pp 291 and 293 § Ibid vol i pL 1 - - 36932821 113687 51125 Page 92 Text v 3 http //www biodiversitylibrary org/page/36932821 1847 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 3 1847 Geology Periodicals Smithsonian Libraries bhl page 36932821 dc identifier http //biodiversitylibrary org/page/36932821 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-17 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13205993984 2015-08-26 12 55 16 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1847 Photos uploaded from Flickr by Fæ using a script
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