Mil} GYPSUM. 
round to Chellaston, bending back to Castle Donington, thence to 
near Loughboro’, and through the valley which is now the Trent, 
along by Nottingham to Newark and Lincoln. 
The portion of the glacier which passed over the limestone as 
-well as the overlying rocks took that substance with it, and dropped 
it chiefly about the water line, and piled it up in irregular masses as 
glaciers terminating in the sea do to-day. 
It is thus we find the massive Gypsum at present. It naturally 
does not occupy the whole of the ice line, but is found in the direction 
of the flow of the limestone, and his again been washed away in some 
places by more recent changes. Other portions of the water line are 
occupied here and there with boulders of other material derived from 
the Yoredale shale, the Breccia, and the Magnesian Limestone, but 
most of these have disintegrated and have gone, in part, to the form- 
ation of the Keuper, New Red Marl, etc., and, finally, some of the 
more recent beds. 
We have now got as far as a working hypothesis of the source 
of one of the constituents of massive Gypsum, viz: the lime. Whence 
did the other constituent come ? 
When the limestone was being brought down by the glaciers, 
the coal of the coal measures was being denuded also, and no doubt 
aqueous denudation took place upon the same lines immediately 
afterwards, and, indeed is going on now. What can coal have to do 
with the matter? I will try to show you! You have all noticed 
the very common occurrence of “‘ brasses” in a lump of coal. If we 
compare the ‘‘ brasses” of the coal with specimens of iron pyrites, 
or iron disulphide, we shall see that they agree in appearance, colour, 
brightness, etc., and analysis has shewn that they are identical. 
Having had to deal with various samples of pyrites, I noticed that 
some of them began to disintegrate, and that the disintegrated sur- 
faces were covered with greenish-grey crystals, with slight drops of 
water containing free acid. On examination, the crystals were 
