Dr. Irving — The Malvern Crystallines. 453 



it being a rare thing to find either the granite or the diorite display- 

 ing anything like a dyke-relation to the other, the few cases in 

 which there is a semblance of such a relation being perhaps best 

 explained by internal stresses setting up slight local shearing-move- 

 ments (under the influence of gravitation and perhaps other forces) 

 along planes or zones of weakness in the rock-mass caused by 

 unequal contraction of the more acid and the more basic portions during 

 congelation. (The gradation from diorite through a biotite- or horn- 

 blendic- granite to a very coarse pegmatite may be seen at West 

 Malvern near the church.) 



2ndly. Upon the way in which the felspathic and the quartzo- 

 felspathic veins ramify in all directions through the diorite, as 

 pointed out long ago by Phillips {loc. cit.). (North Hill, and the 

 quarries at North Malvern and at the Lower Wych, afford excellent 

 examples of this relation.) 



Srdly. Upon the fact that very often the hornblendic rock is 

 observed to be more completely basic in immediate contiguity with 

 the felspathic veins ; whereas we should expect the contrary to be 

 the case, if the latter were injected veins. 



4thly. Upon the very significant fact, that the quartzo-felspathic 

 veins, even when less than an inch in thickness, have a coarsely- 

 granular texture, this being so manifest macroscopically (especially 

 when the rock is slightly weathered) as to make it impossible to 

 believe that they crystallized in contact with a colder rock after 

 injection into it. 



On the other hand, we may perhaps understand the facts observed, 

 with the light thrown upon them from the rate of solidification 

 of basic and acid slags observed years ago by Macfarlane.-" The 

 observed field-relations of the Granite- diorite series at Malvern 

 seem to accord with his observations on slags, which warrant the 

 hypothesis that the more basic portions of the magma solidified 

 more rapidly and at a higher temperature than the more acid veins, 

 the latter continuing for a long time in a viscous condition,- in which 

 condition they would of course act as " lubricating material" between 

 the already solidified basic portions, allowing easy relative move- 

 ment of those parts, as the result of internal stresses, set up within 

 the mass. It is possible that in this way many cases of schistosity 

 observable in some of the felspathic veins may have been produced 

 at that stage of their history. The author feels the more justified 

 in putting forward this view, from the differentiation of structure 



* See " Canadian Naturalist " for 1864, quoted by the present writer in "Met. 

 of Rocks," page 70 (footnote), " On the Origin of Eruptive and Primary Rocks," 

 by T. Macfarlane, now chief Analyst to the Dominion Government. It is instructive 

 to note the revival of the ideas of Macfarlane and Naumann in the "New Geology," 

 as the fogs of ' ' regional dynamic metamorphism ' ' clear away. 



'■* What the late Dr. Percy called " pasty fusion." See "Fuel, etc.," page 63. 

 Macfarlane's observations of the wide range of temperatures, which holds good for 

 this condition of "pasty fusion" in acid slags, extending both above and below the 

 temperatures at which the more limpid basic slags rapidly congeal, explains how in 

 some cases thin felspathic veins appear to fill fissures in the already solidified, but 

 still hot, amphibolitic rock-masses In this sense some of them may, perhaps, be 

 regarded as " injection-veins." But they are a minor feature in the Malverns. 



