488 PUOF. T. G. HONNEY AND MAJOR-GEN. C. A. M*=MAHON 



border of, or are partially replaced 1)}% secondary hornblende. Here 

 and there, in otlier parts, and iu the ordinary ^rts^?'-gabbros, some 

 trace of the original diallage may be found amid a crowd of horn- 

 blende grains * ; the former occasionally exhibit some traces of 

 mechanical disturbance, such as a slight bending of the cleavage- 

 planes or pinching up of an end. These indications, however, are 

 suggestive of a strain, due to a tensile movement of the mass rather 

 than of a crushing down of the grains. The cleavage-planes in the 

 different grains generally, but not always, exhibit a tendency to 

 parallelism. 



The saussuritic constituent is at times fairly clear and transparent, 

 at times brownish, varying from moderately translucent to almost 

 opaque. The former, with crossed nicols, appeal's as aggregates of 

 rather bright-coloured specks, and the original mineral seems to 

 have occurred in rather polygonal grains, often about '01 inch in 

 diameter ; traces of this structure also can be occasionally de- 

 tected in the more opaque patches. It might be argued that this 

 " mosaic " is a proof of crushing, but the uniform general distri- 

 bution of the structure appears adverse to this idea, and it might be 

 explained either as the result of secondary change in an original 

 larger felspar grain f , or as an original microgranular structure X' 



This more opaque part occurs in irregular rounded patches, in 

 rudely rough-edged oblongs, or in streaky clots. Assuming them 

 to represent a felspar of slightly different composition, as is rendered 

 probable by their mode of occurrence, these patches on the whole 

 are not at all suggestive of crushing, for though the last mode of 

 arrangement might be so interpreted, it would be equally possible 

 with a fluxion-structure. 



(c?) Near the Spernic Arch there are several thin veins of com- 

 pact diorite intrusive in gabbro. One of these veins, about two feet 

 thick, splits up into minor veins a few inches thick, which run with 

 the foliation of the gabbro in a way that reminds one of the alter- 

 nating white and black parallel bands of the granulitic series ; but 

 when the dioritic veins are followed up, they are seen to cut 

 obliquely across the foliation of the gabbro at a low angle. Yet 

 though the gabbro is intensehj foliated, the compact trap does not 

 give, under the microscope, any indication of crushing or any more 

 parallelism of structure than is usually presented by the flow of 



* A white or very pale augite in roiiudish grains is present in some examples, 

 t Prof. Jufld on the replacement of labradorite by scapolite, Min. Mag. 

 vol. viii. p. 18G. 



\ I collected, during a visit to the " norite region," N. of St. Jerome in Canada 

 (in 1884), a specimen of a fine-grained norite, which showed on weathered sur- 

 faces a faint structure much )*esembling a fluxion-structure. Microscopic 

 examination shows that the felspar (which is well preserved) occurs chiefly in 

 small polygonal grains (about the above-mentioned size), mixed with larger 

 grains, often about three tiuies the diameter, but sometimes more. The mass 

 does not give the slightest hint of having been crushed, and we appear to have 

 a record of crystallization in ^22*?^ analogous to that of a microgranite. The 

 pyroxenic constituent, which is not abmidant, is less well preserved, and 

 irregular in outline, but appears to have formed, as best it could, i7i situ. — 



T. a B. 



