42 BULLETIN OF THE 



was observed in various places. One specimen is seen to be composed 

 of augite, hornblende, feldspar, viridite, titaniferous iron, and epidote 

 (243+). The augite is much altered, changed to viridite and hornblende. 

 Another section (283) shows no augite, this mineral being entii-ely re- 

 placed by the secondary hornblende. The feldspar is so greatly changed 

 that only part of it shows its triclinic character. Of a similar character 

 to No. 283 are Nos. 238+ and 239+, from the " diorite " south of Lake 

 Superior mine, neither showing any augite, although the hornblende is 

 doubtless secondary, as in the others. No. 239+ is more coarsely crys- 

 talline and granitoid in its structure. 



The "diorite" (180) lying between the Lake Angeline and Salisbury 

 mines is seen in the thin section to be composed of plagioclase, horn- 

 blende, biotite, epidote, viridite, and titaniferous iron with its alteration 

 product. Of these only the feldspar and titaniferous iron are appar- 

 ently original constituents. 



The diabase (175) forming the southeast side of the Salisbury mine 

 is a dark gray crystalline rock, holding ledge and tabular formed crystals 

 of feldspar, and weathering to a rusty brown. It makes a most beauti- 

 ful section under the microscope when studied in polarized light. It is 

 composed of plagioclase, orthoclase, augite, magnetite, olivine, viridite, 

 and hematite. The plagioclase cuts through the augite, leaving it in 

 cuneiform and irregular masses. The olivine is in rounded and irregu- 

 lar grains of prior origin to the crystallization of the rock, and is held 

 both in the feldspar and in the augite. It holds a similar relation here 

 to the feldspar that it does to the enstatite in the Presque Isle peridotite. 

 While the central portions of the olivine are sometimes clear and un- 

 changed, the grains are generally altered to a greenish or brownish ser- 

 pentine. A little fissure traverses the section, cutting and connecting a 

 number of the olivines. This fissure can be readily traced under the 

 microscope on account of its having been filled throughout its extent with 

 the greenish serpentinous material derived from the olivine. The feld- 

 spar is in some cases nearly filled with stone inclusions, arranged parallel 

 to the crystalline faces. These inclusions are evidently inclusions of a 

 devitrified base. This dike is said to ascend by steps, not in a straight 

 line. • 



Near Deer Lake, northwest of Ishpeming, a " diorite " dike running 

 N. 45° W. (231) was seen cutting a breccia and conglomerate (229, 

 230). This "diorite" is so altered that it resembles a chlorite schist, 

 and in the thin section is seen to be composed of chlorite, quartz, nnd 

 mica. It holds some ferruginous masses resembling the product of 



