34 8 SCIENCE PROGRESS 



times disappears ; and it is difficult then to say how much of 

 their crystalline constituents is original, and how much is 

 derived from delicate interpenetration by the granite. The 

 high degree of intermixture is astonishing when the microscope 

 is brought into action, and the darkening of the granite near 

 the contact is clearly connected with the absorption of material 

 from the schists into which it has intruded. 



Surely, then, where the same granite shows a banded 

 structure parallel with the foliation of the adjacent schists, 

 this may be, and very probably is, due to the presence of 

 residual flakes of the schist, only partly " granitised," remain- 

 ing along and near the contact-zone. If, moreover, as is here 

 the case, the foliation of the schistose rocks represents the 

 original bedding of a sedimentary series, the corresponding 

 foliation in the granite is a relic of, and is induced by, the 

 same original stratification. Whole masses of granite may 

 thus invade and take the place of a pre-existing schistose 

 series, without destroying all traces of the original structure 

 of the district. This is the extreme case of the phenomenon 

 of lit par lit injection, so ably described and explained by 

 Michel Levy, 1 and so adequately illustrated by Barrois, Lacroix, 

 and other workers in French metamorphic areas, from Brittany 

 to Mont Blanc and the Pyrenees. Levy's own work on the 

 granite of Flamanville 2 is a convincing exposition of the 

 phenomena of marginal alteration and absorption ; while in 

 Great Britain, Miller, 3 in dealing with certain Scottish granites, 

 has gone so far as to write that parts of these granites " are in 

 fact pseudomorphs, or granite casts, preserving, as replacement 

 structures, remains of the structure of the pre-existing rock." 



Put in some such form as the above, and accompanied by 

 demonstration of the phenomena in the field, it is easy enough 

 to persuade the geological student, unacquainted as yet with the 

 literature of metamorphism, of the correctness of Levy's view 

 in a wide series of examples. Take this embryo observer from 

 Donegal, where the same type of granite-contact occurs over 

 hundreds of miles of boundary, and set him in the county of 



1 " Sur Forigine des terrains cristallins primitifs," Bull. Soc. gcol. de France, 

 1887. 



2 Bulletin Carte gcol. de France, tome v. (1893). 



3 Quoted by Home and Greenly, " On Foliated Granites and their Relations to 

 the Crystalline Schists of E. Sutherland," Quart. Journ. Geol. Soc. London, vol. lii. 

 (1896), p. 635. 



