154 NEW YORK STATE MUSEUM 



aside from color, there appears to be no difference in character 

 between the red and green materials. Although the spots are very 

 irregularly arranged they are, nevertheless, pretty uniformly dis- 

 tributed throug'h the whole mass of red shale, and it is estimated 

 that they make up less than 2^ of the mass. Another fact of im- 

 portance is the frequent presence of dark to black centers in the 

 green spots. Such dark centers which are particularly well shown 

 in Kirkland glen, range in diameter up to a half inch and they are 

 rarely concentric. A much lighter shade commonly extends from 

 the black center well out toward the periphery of the green spots. 

 These dark centers are certainly organic, the dark color being com- 

 pletely removed by heating before the blowpipe. 



After treating the green spot material with hot hydrochloric 

 acid a green glauconitic residue is left precisely like that from 

 the red shale. Ferrous iron has gone into solution as shown by 

 the heavy blue precipitate with potassium ferricyanide. Am- 

 monia, however, fails to give the brown precipitate for ferric 

 iron, while sulphocyanate gives only a slight coloration. This 

 coloration is doubtless due to the fact that by infiltration a 

 small amount of hydrated ferric oxid has comparatively re- 

 cently been mixed with the green spots. Ferric oxid is, there- 

 fore, practically absent from the green spots. According to an 

 analysis made by Dr A. P. Saunders, a sample of the green spot 

 material contained 1.19^ of ferrous iron obtained from the dilute 

 sulfuric acid solution. The writer believes that the ferrous 

 iron is largely present in the carbonate form. Both the red and 

 green shale when treated with cold hydrochloric acid show al- 

 most no sign of chemical action but after warming a vigorous 

 eft'ervescence sets up and this suggests iron carbonate. This car- 

 bonate doubtless forms the rhombohedral crystals seen in thin sec- 

 tion. 



Many years ago Vanuxem^ described these green spots and 

 stated that : '^ It is not easy to resist the impression that the 

 green color is the result of a change in the red particles, the 

 peroxid of iron being reduced to a protoxid." He makes no 

 mention of the black organic centers. His view is still com- 

 monly held but there are certain objections to it as for example the 

 highly improbable assumption that the red color was original and 

 the fact that the chief coloring matter in the green shale is glau- 

 conitic and not protoxid of iron. 



'Geol. 3d Dist. N. Y. 1842. p. 97. 



