GNEISSIC FOLIATION. 123 



character of some of the archean rocks, especially if by careful re- 

 search and accumulation of evidence it be found possible to extend 

 them from the special to the general. If from admitting the develop- 

 ment of a gneissic foliation in an undoubted igneous rock we admit 

 the possibility of the great Laurentian system of rocks which are 

 granites or syenites in composition but gneisses in structure, having 

 been in a fluid state, we take a great step towards removing the ne- 

 cessity for a theory of metamorphism which ascribes a sedimentary 

 origin to these rocks. It may, indeed, be urged that the metamor- 

 phic theory admits a once viscid condition for these rocks and that 

 this state was only the extreme of metamorphic action, but the 

 moment the theory admits this it removes at once its raison d'etre 

 and becomes a far-fetched and cumbersome hypothesis to explain 

 phenomena that can be accounted for in a far simpler way. For it is 

 absurd to admit the development of a gneissic foliation in a granitic 

 rnagma whose fluid condition has been brought about by the action 

 of hoat on once solid strata, and to deny the possibility of a similar 

 differentiation in the original granitic magma or fluid, which is 

 generally conceded to have constituted the first surface of our globe. 

 The development of a foliation in a magma which is such ah origine 

 is as easily conceivable as that in a magma which is only such 

 secondarily, and is far simpler as a scientific hypothesis, in the fact 

 ttiat it avoids the necessity of imagining an immense process of sedi- 

 mentation of a most peculiar cLai'acter, and leaves us as far as ever 

 from the beginning in attempting to trace out the history of the 

 earth's crust from the time of its molten state. 



As a general rule, however, the exponents of the metamorphic 

 explanation of the archean rocks do not carry their contentions quite 

 so far as this. The Laurentian gneisses, they say, are sedimentary 

 rocks, which, though in the process of metamorphism they have been 

 reduced to a plastic condition, have never been rendered so com- 

 pletely homogeneous as to lose all traces of sedimentation, which 

 traces are manifest in the parallelism of the planes of crystalline 

 foliation ; further, that many granites are but gneisses that have 

 undergone this extreme stage of metamorphism and so had these 

 traces of sedimentation quite obliterated. This of course puts the 

 question on much more debatable ground ; but if it can be shown 

 that, in true igneous rocks, which, if our ordinary conce[>tions of 

 intrusive phenomena are to stand, must have been in the condition 



