4.4, ANALYSIS OF A PICTOU COAL SEAM—GILPIN. 
contain them in varying proportions, sometimes to such an 
extent that the coal is rendered valueless for economic purposes: 
Almost the only value these bands of shale possess, is their 
record of the progress of growth of the associated coal. Applying 
the record of the numerous small bands of shale and shaley coal 
found in the seam under consideration, we learn that the growth 
of this deposit was not an uninterrupted one. Searcely had the 
vegetation for a few inches of coal been accumulated, when a 
change took place, and it was covered by a layer of mud. 
It is useless, perhaps, now to speculate how this covering 
was formed, perchance the shelter of some bar was broken, and 
for a season the tides could deposit their burden, .or some name- 
less river of bygone days became obstructed and flooded the 
swamps, in which grew the weird vegetation of the carboni- 
ferous era. 
Then, again, the vegetation accumulated to be once more 
interrupted. The presence of layers of coarse and shaley coal 
shows that the transition from a flourishing vegetation to a 
mud-laden flat was, in some cases, a gradual one, due, perhaps, to 
periodic inundations. Similarly the return te the conditions 
favourable to the growth of the coal plants was sometimes a 
slow one, as the struggle between land and water was year after 
year more and more in favour of the vegetation. 
Thus grew our coal deposits, subject to the fluctuations of 
the district, and when the miner’s pick thus reveals page after 
page of this wondrous history, it is not unreasonable to hope that 
some time they will be deciphered even more readily and with 
greater certainty than the changes now progressing around us. 
So far as I am aware, it is noticeable that in all seams 
these layers are composed of very fine material, that never 
have the conditions of growth been so abruptly altered as 
to allow gravel or conglomerate to intervene. Such inter- 
calations might, however, be observed in seams formed on 
the edges of productive districts where changed physical 
conditions held sway. So strongly marked were the general 
conditions of wide spread. levels of vegetation during the pro- 
ductive period, that we find, even when oscillations permitted 
