328 THE JOURNAL OF GEOLOGY. 



means accurately describes it as a whole. At a locality cited by 

 Sir William Logan, as one where it is typically developed, namely, 

 Trembling Mountain in the above mentioned Grenville Area, it 

 consists of a fine grained reddish orthoclase gneiss, with distinct 

 but not very decided foliation, containing here and there bands 

 of orthoclase gneiss of somewhat different character; as well as 

 bands or layers of a dark amphibolite. 



How much of this Fundamental Gneiss really consists 

 of eruptive material is not known. The indistinct foliation, 

 in many cases at any rate, is not a survival of original 

 bedding, but is clearly due to movements in a plastic mass. It 

 is often possible to recognize the existence of an indistinctly 

 foliated gneiss intruded into more distictly foliated gneiss. The 

 gneiss, in some cases, shows excellently well-marked cataclastic 

 structure, while in other cases this is not distinct. The evidence 

 accumulated goes to show that the Fundamental Gneiss consists 

 of a complicated series of rocks of unknown origin, but com- 

 prising a considerable amount of material of intrusive character. 



The Grenville Series. — In certain parts of the Laurentian area, 

 and notably in the Grenville district before mentioned, the Lau- 

 rentian has a decidedly different petrographical development. 

 Orthoclase gneiss is still the predominating rock, but it presents 

 a much greater variety in mineralogical composition, and is much 

 more frequently well foliated, often occurring in well defined 

 bands or layers like the strata of later formations. 



Amphibolites are abundant, also hornblende schists, heavy 

 beds of quartzite and numerous thick bands of crystalline lime- 

 stone or marble, all these rocks being interbanded or interstrati- 

 fied with one another. In the vicinity of the limestones the 

 variety in petrographical character is especially noticeable ; garnets 

 often occur abundantly in the gneiss, the quartzite and the horn- 

 blende schist, as well as in the limestone itself, beds of pure 

 garnet rock being found in places. Pyroxene, wollastonite and 

 other minerals are also abundant, while the presence of graphite 

 disseminated through the limestones and their associated rocks, 

 often in such abundance as to give rise to deposits of economic 



