MACKAY ON MANGANESE DENDRITES. RK KLE 
the microscope demonstrated the entire absence of organic structure. 
The specimen came from the neighborhood of St. Mary’s Bay, Digby 
Se & 
MANGANESE DENDRITES ON RED SANDSTONE. 
(Reduced to one-fifth of linear dimensions.) 
county. The structure of the flag showed that these Manganese den- 
drites were originally formed between two close layers of the original 
flagey sandstone. He suggested as an explanation of the dendritic form 
of the manganese deposit, the observed fact that when a thin sheet of 
liquid holds in solution certain substances, and from any cause the 
solution is becoming supersaturated, these substances, if they have a 
tendency to crystalize, are not precipitated uniformly like ordinary 
sediment. The precipitation commences at a point where the super- 
saturation begins to develope, which, let it be supposed, in the thin 
plane of cleavage in the flag, was near the outer margin where the 
deposit salt first made its appearance. Assuming the crystaline attrac- 
tive force to operate effectively at a distance of, say, the eighth of an 
inch, the precipitating material would congregate from that distance to 
the first point of deposition, leaving a clear space of that extent on each 
side. And as the supersaturation extended inwards, the point would be 
extended into a line. But, assuming that the wave of supersaturation 
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