694 THE GEOLOGY OP MINNESOTA. 



[Diabase. Amphibolyte. 



richer in hornblende. The excavation passed through the iron-bearing member of 

 the Animikie and struck granite. 



Age. Archean. u. s. G. 



No. 1329. DIABASE (with olivine) . 



About one-eighth of a mile west of the northeast corner of sec. 22, T. 65-4 W. 

 Ref. Annual Report, xvi, pages 81, 121 ; Annual Report, six, pages 195, 201. 



Mey. An ordinary diabase, looking like the diabase of the Logan sills in the 

 adjoining Animikie strata. No section. 



Mic. W. S. Bayley's description of this rock is as follows:* 



" This specimen is a sample of a great dyke that cuts the gneiss underlying the 

 rocks above mentioned. No. 1329 does not correctly represent the dyke, but it is 

 the only sample that has been furnished. It is a very coarse-grained olivine-diabase, 

 with long, lath-shaped crystals of a plagioclase near andesine, large grains of light- 

 colored olivine, and interstitial, allotriomorphic, dark pink, slightly pleochroic augite, 

 with much irregular magnetite. in and around the augite. This last named mineral 

 is quite fresh, except in small areas immediately next to feldspars, where it is 

 slightly chloritized. The rock resembles very strongly the substance of the great 

 dykes everywhere cutting the Animikie in the lake Superior region." 



Age. Probably Cabotian dike cutting Nos. 1330 and 1331. u. s. o. 



No. 1330. AMPHIBOLYTE. 



Near the quarter post between sees. 20 and 21, T. 65-4, west of Gunflint lake. 

 Ref. Annual Report, xvi, pages 82, 83, 121. 



Meg. Greenstone, harsh, firm, hornblendic. 



Mic. The rock consists almost exclusively of well crystallized hornblende, with 

 the angle cAc (maximum) measured on 010 at 20. It has n p as the acute bisectrix. 

 There is, however, a sprinkling of magnetite throughout some of the larger grains. 

 One section. 



Age. Archean (Keewatin). N. H. w. 



No. 1331. AMPHIBOLYTE. 



Prom the same place as No. 1330. 



Ref. Annual Report, xvi, pages 82, 121. 



Meg. Green schist, schisted condition of No. 1330. 



Mic. Like the last, but finer and containing a considerable feldspar. There are 

 also isotropic, brown areas (biotite) elongated with the structure, in which appear 

 small biotite scales. One section. 



Age. Archean (Keewatin). N . H . w. 



* Nineteenth Annual Report, p. 195. 



