SIXTH REPORT OF THE DIRECTOR I909 1 55 



Maw,^ in referring to green spots in general, stated that : 

 " The generally accepted theory, and that suggested by De la 

 Beche in explanation of the phenomenon, is, that the discolora- 

 tion has been brought about by the reduction of the sesquioxid 

 to a lower state of oxidation of less coloring power by simple 

 chemical reaction with the fossil carbon." The objections above 

 given apply in this case also but the influence of the organic 

 matter is here clearly brought out. As early as 1831 Fleming^ 

 recognized the agency of decomposing organic matter in the 

 production of the light colored (but not green) spots in the Old 

 Red Sandstone. 



It is well established that decomposing organic matter will 

 effect the reduction of ferric to ferrous iron and the organic 

 matter in the green spots of the Vernon shale has no doubt 

 caused such a change, but since, in this case, the ferric oxid 

 was in the hydrated state and hence not red, it is not correct to 

 say that there was a change in color from red to green. Rather 

 the writer believes that the presence of the organic matter has 

 simply prevented the appearance of the red color in the immedi- 

 ate vicinity because the oxid of iron has here all been reduced 

 to the ferrous condition. Within the spots, then, the green 

 color of the glauconite is allowed to come out, and it is this 

 rather than the small percentage of iron in the ferrous condi- 

 tion which gives the green color. In each case the size of the 

 green spot has been directly dependent upon the amount of the 

 decomposing organic matter. The presence of ferrous iron in 

 both the red and green shales may be readily explained be- 

 cause this iron is probably mostly in the carbonate form which 

 would be pretty freely disseminated through the whole shale 

 mass. 



Origin of color in the green shale. In view of the above state- 

 ments the explanation of the origin of the color in the green 

 shales, at the base and the summit of the red shale, becomes a 

 comparatively simple matter. The character of the material 

 in the green shale is, in every way, like that in the green spots 

 and the explanation of the origin of the color in the spots may 

 be applied here also. In this case, however, the organic mat- 

 ter was probably more abundant or, at least, it was more finely 

 divided and scattered through the mass so that all of the ferric 



^op. cit. p. 371. 



^"Old Red Sandstone'' by Hugh Miller, quoted on p. 235. 



