130 THE GEOLOGY OP MINNESOTA. 



[Amygdaloid. Concretions. 



No. 34. AMYGDALOID. 



Duluth. Near the mouth of Chester creek. 

 Ref. Annual Report, ix, pages 16, 20. 



Overlies No. 33B, and is about fifteen feet thick, the two passing gradually into 

 each other across the bedding. This is a beautifully specked and spotted amygda- 

 loid, some of the concretions being white (one-half to one inch across), some red 

 (one-fourth to one-half inch), some green (one-fourth inch), and some with a red 

 centre enclosed in a green coating. The rock itself is so altered that it is impossible, 

 in the thin section at hand, to identify the original minerals. It can only be said 

 that a reddened twinned plagioclase whose general forms are still sometimes quite 

 distinct, is distributed idiomorphically amongst the other minerals. The matrix 

 consists of chlorite, magnetite, altered glass, hematite, quartz. 



Two poor, very small sections examined. 



Age. Cabotian. N. H. w. 



No. 34A. CONCRETIONS, ETC. (from No. 84). 



Ref. Annual Report, ix, page 16. 



The red amygdules are colored by h<>nt<ttU<', which seems to be distributed with 

 slight reference to any crystalline structure or form. It is occasionally in parallel 

 or radiating coarse fibres. The rest of the section is largely made up. of a light- 

 greenish chloritic substance which is so fine that it appears dark, like an amorphous 

 substance, or when coarser affords an aggregate polarization. This chloritic sub- 

 stance pervades the whole mass, except where a few grains of quartz or of calcite 

 have been generated. The hematite seems to be distributed through this chloritic 

 substance. With the exception of a few irregular grains of muynrtifc and of i-pnloh- 

 which are independent of the hematite, this constitutes the nature of these red amyg- 

 dules. The white concretions are of quartz or partly of m/rifr. 



In some parts of the slide the forms of the hematite indicate that it has taken 

 the place of some fibrous or radiated mineral. Some of these amygdules, when 

 stained red, have a calcite matrix, which, when they are broken, shows its cleavage 

 distinctly. Both the calcite and the quartz sometimes embrace the red material-in a 

 micro-poikilitic manner. 



Two sections examined. 



Age. Concretions in Cabotian surface lava. N. H. w. 



No. 35. DIABASE (with olivlne). 



Duluth. Near the mouth of Chester creek, on the west side. 

 Ref. Annual Report, ix, pages 16, 17. 



Meg. A hard, reddish imperfect amygdaloid, with numerous natural seams 

 which cause it to part easily in all directions without affording a fresh fracture; a 



