800 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Silica 46.48 



Alumina 17 71 



Protoxide of Iron . . 21.17 



Lime 9.89 



Magnesia trace 



Alkalies by difference . 1-97 



Water 2 78 



100.00 



Mr. Macfarlane says : " It fuses before the 

 blowpipe to a black, slightly magnetic glass. 

 On ignition it changes to a light yellow color, 

 losing 04 per cent of its weight. It is decom- 

 posed by hydrochloric acid, and the resulting 

 solution contains protoxide, as well as perox- 

 ide of iron." In the analysis the iron was 

 calculated as protoxide, and the difference 

 . between it and peroxide put down as water. 



It seems possible that, at least, much of the lime was due to inter- 

 mingled calcite ; for I found, under the microscope, calcite particles in 

 the powder scraped carefully from the amygdules of the Pewabic 

 occurrence. 



Between crossed nicols this mineral appears to be orthorhorabic ; with 

 one nicol it shows feeble dichroism. It is, probably, one of the many 

 minerals for which we have as yet no better general name than green- 

 earth. 



There can be little doubt that here, as in the specimen from the 

 Ossipee amygdaloid, the matrix has been prehnitized, and the prehnite 

 changed to pseudo-amygdaloidal chlorite, while the prehnite of the 

 amygdulea, small and large, was changed to epidote and orthoclase. 



Amygdaloid from Section 8, Town. 47, Range 45. — Some interest- 

 ing specimens, illustrating the change of prehnite into epidote and 

 orthoclase, were collected by me in the Southern Copper Range at 

 400 paces north of the east \ post of Section 8, Town. 47, Range 

 North, 45 west, in the southern part of Ontonagon County. The 

 rock is an amygdaloid with a fine grained gray -green matrix. It 

 contains numerous small amygdules of compact dark-green pseudo- 

 amygdaloidal chlorite, and many large spike amygdules sometimes two 

 or three inches long, and \ inch or less in diameter. Some of these 

 are filled wholly with epidote, others with epidote as the older, and 

 quartz as the younger member. In some, one portion of the spike 

 consists of epidote, while the rest is the same dark-green chlorite that 

 forms the small amygdules. More rarely the larger amygdules consist 

 of red orthoclase, generally with quartz as a younger member. None 

 of the amygdules are drusy. The epidote is in massive acicular aggre- 

 gates, its structure converging towards the centre. The orthoclase and 

 quartz are in granular aggregates. 



In a thin section of the matrix we see that the greater part of the 

 plagioclase still shows the twin striation in polarized light. There is 

 some unaltered pyroxene, but none of the characteristic pseudomorphs 

 after this. The section contains some pseudo-amygdules of the charac- 



