30 J. CLIFTON WARD ON THE GRANITIC, GRANITOID, AND 



likewise different. It is, indeed, hard to suppose that the matter 

 forming the root of a volcano could exist in a state of igneous fusion 

 without at the same time absorbing into itself portions of the sur- 

 rounding rocks in various degrees, thus having its character more or 

 less modified. 



In this connexion it is well to remember that a granitic mass 

 formed by metamorphism of rocks in situ is almost sure to become 

 an intrusive mass at some part, even among rocks of a similar kind 

 to that out of which it has been formed. 



2. How far Granite may he an ultimate universal product of Meta- 

 morphism. — It has been seen that in the Lake-district there is one 

 group of rocks (the volcanic) which in many of its members (espe- 

 cially the ashes) approaches the granites very nearly in chemical 

 composition, while there is another (the Skiddaw Slate) which 

 generally differs more widely, though having some parts much more 

 highly silicated than others. Now what is true of the rocks of this 

 limited district is true also of rocks in general ; and we might be in- 

 clined to say decidedly that the latter group could not be metamor- 

 phosed into granite, while the former might be. But metamorphic 

 action is varied ; and although a simple melting down of clay-slate 

 might never produce granite, yet a moist fusion, accompanied by 

 elementary substnecs, brought upwards from still greater depths, 

 might effect a great transformation. We know, indeed, that our 

 slate-rocks are often abundantly seamed with veins of quartz, which 

 mineral must have arisen from below in a state of solution, as is 

 evidenced by its now containing myriads of liquid cavities. Now, 

 just as silica has permeated these slightly altered rocks, so we may 

 suppose silica to permeate, probably in still greater quantities, those 

 rocks more highly altered at a greater depth, and the masses in a 

 state of aqueo-igneous fusion at a greater depth still. Hence a rock 

 of the composition of slate may be converted into granite by under- 

 going a change in the arrangement of the elements preexisting in it, 

 tor/ether with the addition from below of some of those elements 

 which were lacking in the original slate. In this sense, for ex- 

 ample, the Skiddaw granite might be metamorphic in its origin, 

 though possibly formed out of lower beds than those among which 

 it now lies, and with the addition from below of an additional quan- 

 tity of silica. 



All writers on metamorphism have agreed that there are but three 

 ways in which it can be effected — (1) change in the mechanical 

 arrangement of the particles, (2) change in the arrangement of the 

 chemical elements, (3) withdrawal or addition of some of these 

 elements. 



3. Distribution of Metamorphism. — There is, perhaps, no more 

 striking geological fact than the manner in which, over highly me- 

 tamorphosed areas, beds or tracts of rock showing little alteration 

 alternate with others most intensely metamorphosed. I believe 

 that the study of alterations effected in such a series of rocks as the 

 " volcanic " in the Lake-district throws light upon this point. In 

 this case there are frequent alternations of beds of very different 



