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| Keywords: The Quarterly journal of the Geological Society of London (12711436905).jpg 1855 FORBES FOLIATION OF ROCKS 179 <br> sideration as being in some cases the agent in causing as well as <br> modifying foliated structure <br> Whatever may he the cause of the arrangement of foliation in cer- <br> tain directions I believe that most geologists agree in supposing that <br> fohation itself is due to the action of heat which has reduced the <br> rock in situ to a fluid or at least semifluid state to which some add <br> the action of gases and pressure <br> On this point I would wish to make some remarks ; and I may <br> premise by stating that to me foliation appears to be the result of <br> chemical action in recombining the elements existing in amorphous <br> sedimentary rocks together with a simultaneous molecular move- <br> ment of the products thus formed ; also that this action is efi'ected <br> by heat but has taken place at temperatures lower than even neces- <br> sary to change the external form of the masses or to produce any <br> semifusion or even softening <br> As corroborative of this I may refer to fig 10 which Keilhau <br> Fig 10 ” Section of the gneiss in the Island of Jomfruland <br> Norway <br> has also observed and made mention of It represents an appear- <br> ance in the gneiss on the island of Jomfruland <br> Here we have a vein of hornblendic character running across the <br> gneiss and disturbed by the fault AB which throws it downwards <br> On examining the lines of foliation it will now be found that those <br> lines which are most distinct are not at all affected by the fault and <br> continue throughout with the greatest regularity ; so that it can <br> hardly be doubted that the foliation of the gneiss took place later <br> than the formation and subsequent dislocation of the hornblende vein ; <br> and consequently we cannot suppose that the mass could have been <br> in a fused or softened state at the time of fohation without the <br> obliteration of these appearances Again referrmg back to fig 8 <br> p 177 it will be seen that the fault b the origin of which apparently <br> was previous to or simultaneous with the granite-vein has altered the <br> position of the foliation on the one side and bent it upwards The <br> faults c D and e do not effect this at all <br> If however the rock had been in a semifused state when foliation <br> took place or when the granite-vein was injected we should have <br> Norske Magazin for Naturvidenskab vol iii p 175 <br> o2 35614751 110213 51125 Page 179 Text v 11 http //www biodiversitylibrary org/page/35614751 1855 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 11 1855 Geology Periodicals Smithsonian Libraries bhl page 35614751 dc identifier http //biodiversitylibrary org/page/35614751 smithsonian libraries Information field Flickr posted date ISOdate 2014-02-23 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12711436905 2015-08-26 20 51 00 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1855 Photos uploaded from Flickr by Fæ using a script | ||||
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