qo The Ottawa Naturalist. [Aug-ust 



shaped crystals of plagioclase now almost entirely altered to 

 rhombohedral carbonates ; also phenocrysts of some ferro- 

 magneslan constituent now completely altered to a mixture of 

 rhombohedral carbonates, quartz, chlorite and oxide of iron. The 

 rock shows a few vesicles now completely filled with decompo- 

 sition products, such as chlorite and ca'.cite. A few well defined 

 hexagonal crystals of fresh apatite of larg;^e dimensions occur 

 scattered through the groundmass, also a few veins of calcite. 



No. 8. — Fine-grained grey rock from Brewer Creek, Upper Kettle 

 River. 

 '* About one mile from the mouth of Brewer Creek and in line 



with the foothills, there is an outcropping of the solid rock forma- 

 tion exposed in the banks of the creek. The formation here seems 

 to be chiefly granite, alternating with dykes of fine-grained basic 

 volcanic rocks, and occasionally, apparently, with still mo.re recent 

 and very acid dykes." 



The sample in question is taken from one of the acid dykes. 



The hand specimen is a dyke rock, medium fine-grained and 

 grey in colour. 



Under the microscope, the rock is seen to be much altered 

 and to be composed almost wholly of altered felspar crystals 

 twinned according to the Carlsbad law, on account of which, as 

 well as from the total absence of albite twinning, they were 

 assumed to be orthoclase. Small narrow laths of biotite a^e 

 abundant, which, however, have undergone C'^nsiderable altera- 

 tion, in most cases being changed to chlorite. Secondary quartz, 

 associated with calcite and apatite, is also noticeable, and, as 

 accessory constituents, magnetite and pyrite. The groundmass, 

 which consists of small felspar individuals, also has a small 

 amount of quartz, possibly secondary, distributed through it. 

 There are a few vesicular cavities filled with zeolites. 



The rock corresponds in character and composition to a 

 minette. 



No. 53. — " Porphyrite from Rebecca Mine, Rock Creek, west side 

 of Kettle River, 4 miles above Rock Creek. Elevation 

 4,000'." 

 " The chalcopyrite is carried by a quartz vein which cuts this 



rock, ^^'^lue of mineral, $22 per ton." 



