936 THE GEOLOGY OP MINNESOTA. 



[Diabase. 



mineral generations. This surrounds the diallages completely, and also partly 



embraces some of the olivines. It has four cleavages, and is plainly pleochroic. 



The diallage has also the four cleavages, viz., two 110 and the vertical pinacoidal 



cleavages. Its small optic angle contains and measures about 45, which is a 



peculiarity of augite seen in the gabbro from the larger masses in the central parts 



of the great gabbro area. The rock embraces but little magnetite. Two sections. 



Age. Cabotian. N. H. w. 



No. 429E. DIABASE (with olivine). 



Top of the high Sawtooth ridge west of Temperance river. 

 Ref, Annual Report, xxiv, page 159. 



Meg. Dark diabase, rather coarse. 



Mic. The augite has a pinkish-purple color and is ophitic in its relation to both 

 olivine and plagioclase, while the olivine has the same relation to the plagioclase, a 

 structure not very common. One section. Compare No. 258. 



Age. Cabotian. N. H. w. 



No. 455E. DIABASE (with olivine). 



Near Poplar river, from the hill west of the hay marsh, and known as " the rock pile." 

 Ref. Annual Report, xxiv, page 159. 



Meg. Dark gray, rather coarse. 



Mic. A coarse ophitic rock, with some olivine, the olivine showing the common 

 alteration along fissures and about the margins, producing the familiar yellow 

 substance which is supposed to represent bowlingite. One section. 



Age. Cabotian(?) N. H. w. 



No. 456E. DIABASE. ( Coarsely porphyritic. ) 



South slope of the first Sawtooth hill north of Lutsen (Poplar river). 

 Ref. Annual Report, xxiv, page 159. (Compare No. 796.) 



Meg. Coarse diabase, with conspicuous tabular crystals of labradorite. 



Mic. The porphyritic plagioclases which are taken for labradorite, are accom- 

 panied by many of the second consolidation. Augite is in rather small amount, and 

 in form of small grains which are for the most part of independent forms, but 

 one is rarely cut by one of the second-date plagioclases. Olivine once existed in this 

 rock, but is now altered to a yellowish substance. Magnetite not abundant. One 

 section. 



Age. Cabotian. N H w 



