124 
dendritic markings radiating from the fissures in the rock, 
and constitutes a portion of the cementing material in many 
of the concretions. 
In the sandstones of the coal measures, also, oxide of 
manganese forms part of the cementing material in many 
of the concretionary structures. 
In fact, careful observations would probably show that 
oxide of manganese is quite as widely distributed as oxide 
of iron, the only difference being that the former mineral 
generally occurs in defined patches and in comparatively 
small quantities. The distributing causes seem to have 
acted as universally with the one mineral as with the other, 
but in the case of the manganese only small amounts were 
concerned, while in the case of the iron there was an almost 
unlimited supply. 
