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may be either coarse or fine grained and of various colours, generally 

 some shade of red or gray. Differences in texture, as well as in com- 

 position, give rise to vai'ieties. Thus, for instance, there is schistose 

 gneiss in which the mica forms continuous, thin, parallel, even lamellae, 

 which separate the granular layers composed of quartz and feldspar, 

 " granitoid gneiss, in which the foliation is very obscure and the rock 

 somewhat resembles granite," and " augengneiss," or eye gneiss, in 

 whicli large individuals of orthoclose are embedded in a somewhat 

 lenticular shape supposed to resemble an eye. 



Tiie great beds of limestone, which, as mentioned above, are often 

 interstratified with the gneiss are generally white, but sometimes have 

 a greyish, pinkish, or salmon colour. They are geiierally coarse grained, 

 but sometimes saccharoidal in texture, and usually contain a number of 

 accessory minerals. In Dr. Hunt's memoir on the Laurentian limestones 

 of North America he enumerates no less than fifty-four mineral species 

 occurring in them. These minerals, especially when found in limestone 

 veins, are frequently well crystallized, and most beautiful combinations 

 are often found, such as bright green apatite, or pyroxene crystals, in a 

 matrix of coarsely crystalline pink limestone. These limestone bands 

 are well exjjosed in the Township of Hull, and in the Grenville region 

 contain the celebrated Ebzoon Canadense. 



Associated with these limestone beds are beds of quartzite, horn- 

 blende schist, pyroxene rock, garnet lock, etc., often of considerable 

 thickness. 



Another class of rocks which are found in many places in the 

 Laurentian system and which are deserving of mention are the so-called 

 anorthosite, labradorite or Norian rocks. These occur not only in 

 Canada but also in Scandinavia, New York, and in the North of 

 Scotland. In Sweden, where they have been most carefully studied, 

 they are in part, undoubtedly, true members of the Laurentian 

 system, while some of the more granitoid varieties are undoubtedly 

 intrusive rocks. They are characterized by the predominence of 

 plagioclase or lime soda feldspar, the frequent occurrence of hypersthene 

 and pyroxene, and the almost entire absence of quartz. A strange but 

 very important fact in relation to these rocks is that, in America at 

 least, the iron ores associated with them are always so far as we at 



