224 



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M. Scheerer attributes what "he calls the "plasticity" of granite 

 when protruded on or towards the surface of the earth (a condi- 

 tion evidenced bj the veins it throws into the fissures of neigh- 

 boring rocks) to the combined action of water and heat. He 

 describes the water as ^^intercalated between the solid atoms of 

 the crystalline and other constituent minerals, endeavoring to 

 escape by its tendency to vaporization, and consequent elasticity, 

 but unable to do so owing to the pressure to which the enclosing 

 mass is subject." He considers the water so contained in granite 

 to be *^ primitive," that is, one of the original bases of the rock, 

 and not the result of infiltration. He attributes to it the solution 

 of the quartz, aided by the alkali, and the consequent moulding 

 of this mineral on the feldspar crystals. He even goes the length 

 of styling the condition of granite before its protrusion by the 

 term '*une bouillie aqueuse," a granitic broth. 



These theoretical opinions of M. Scheerer appear to have re- 

 ceived the assent of M- Elie de Beaumont and other French 

 geologists,"^ Their exact conformity with those which were first 

 ■ eveloped in my treatise on Volcanos, published in 1824-25, and 

 repeated in the preface to my volume on Central France in 

 1826-27^ will be evident to any one who will take the trouble 

 to refer to those w^orks. 



It is not, however, for the vain purpose of claiming a priority 

 in these views, that I now ask the attention of the Society to 

 them, but because the subject has not, I think, yet attained the 

 consideration I think it deserves from the geologists of this 

 country; and especially because of its leading, if followed out, 

 to further inferences of considerable importance/ which were 

 likewise suggested by me in 1825, but have been hitherto only 

 partially pursued to their legitimate consequences. 



Laminated or schistose rocks^ slaty cleavage^ and folded rochs. — I 



refer to the mechanical changes in the texture and structure of 



the plutonic rocks w^hich could not fail to have resulted from the 



mutual friction of the component crystalline particles attendant 



on their internal movements, whether caused by mere dilatation 



and re-compression in place, or by a shifting of the entire mass 



in any direction, under intense and opposite, but irregular pres- 

 sures. 



^ I was led to reflect on this by observation of the ribboned 

 pitchstones of Ponza and Ischia, m which, while in a state of vit- 

 reous fusion, crystallites had formed (just like those of the Old- 

 bury obsidian), and subsequently been broken up bv the move- 

 ment of the semi-liquid mass, and drawn out into long stripes 

 'ving a ribboned appearance to the rock. 

 Further examination proved to me that the ribboned trachytes 

 Ponza and Ischia, and some ribboned clinkstones, owed that 



* See Bulletin de la Soc. Q^ol. France, neuf series, vol. iv, p. 131 3. 



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