OCCURRENCE OF COAL WITH UNUSUAL CONDITIONS 327 
should never, at any stage, extend more than a few yards outward 
from these slopes. This did not happen once only, but a number 
of times, and, furthermore, every time that there was any such 
accumulation, it was very limited. At first it was thought that 
the many thin stringers of pure coal ramifying through the sand- 
stones with no evidence of “‘bottom clays” or old soil beds were 
evidence that the organic muds had been carried in suspension and 
dropped at the points where the coal is now found; if such had been 
the case, it is inconceivable that the mud would not have spread 
at each stage of mud deposition farther to the northeastward 
beyond the limit which was clearly set for it. What this limiting 
factor may have been is not apparent from the deposits themselves. 
As indicated earlier, sand at times accumulated to a small thick- 
ness on the side away from its apparent source, and plant muds 
were interfingered to some extent with this sand; but the coals 
disappear mostly by thinning within a few yards. 
The best explanation for this narrow strip of organic mud extend- 
ing along the margin of the inclined sands seems to be that it grew 
at the point where it is found, and that, at times, the growing plant 
beds spread out for short distances over the sands accumulating 
near by and thus became interbedded with them. The growing 
plants, on this assumption, were confined to the border of a shallow 
body of water and did not spread more than a few yards from the 
edge, although why they should not have spread over much more 
of the bottom which must have been just as shallow is not apparent. — 
The water probably was not nearly of a depth equal to the thick- 
ness of the entire sandstone bed, since the coal is only interfingered 
with its base. In this connection, what the significance of the trace 
of black shale or coal extending up the bedding planes may be, 
cannot be said. It seems quite possible that the level of the water 
was a fluctuating one, standing low during stages of plant growth, 
and high at times of flood when the sands were brought in in large 
quantity. 
It is not intended to imply that the rates of accumulation of 
both sands and muds, in so far as they accumulated simultaneously, 
were equal. On the contrary, the sand was probably dumped in 
