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the bottom, that it had the appearance of stone coal, and the 
properties of shale. A further illustration is afforded in a 
lower pond or lake, where the water has been dried up, and 
the lighter vegetable matter floated away by the upper 
stream. Some of the aquatic grasses have become imbedded 
in the mud or sediment, and there remain to undergo a further 
change under pressure, or become in process of time fossilized. 
Dr. Bevan speaks of the lower measures in the South 
AVales coal field as being anthracite, and the upper as being 
bituminous. At Popplewell, near Low Moor, however, just 
the reverse of this occurs, as below the anthracite there are 
four beds of bituminous coal, and in the cannel coal-bed there 
are two partitions of bituminous shale, which evidently 
indicate that the former has been deposited at three distinct 
periods. It is very common for one kind to run into the 
other, and it is this gradual transition that disproves the 
igneous agency suggested by Professor Rogers ; and to me 
his steam theory is no explanation of the difficulties to be 
solved in accounting for the origin of the different varieties 
of coal, for when the materials are hermetically sealed up 
it is impossible on either theory to produce the change which 
is observable. At the bottom of one of the cannel coal-beds 
at Wigan, there is a bed of shale from one to two inches in 
thickness, and beneath this one or two inches of bituminous 
coal. In the neighbourhood of Batley there is a considerable 
amount of ironstone in the shales, which is almost composed 
of shells, — commonly called the cockle shell roof by the 
miners, and the mussel band of the geologists ; this particular 
roof being over so many of the cannel beds, some of the 
miners imagine one is a necessary accompaniment of the 
other. The Middleton coal has also a similar roof. 
The prevalent idea is that bituminous coal was the only 
kind originally deposited; and that stone coal, anthracite, 
cannel, culm, splint, and glance coal, are the effects of heat 
