298 Natural- Historical Collections. 
endeavours may be seconded by our countrymen, and that his personal ardour in 
the cause may meet with the merited success. 
Kettle bottoms ; foot bottom, or cauldron bottom.—‘‘ In some of the high main 
seam in the great Newcastle coal-field, when the coal is worked away by the 
miners, the roof often falls. This is, to a considerable degree, owing to the 
number of vegetable impressions breaking the coherence of the stratum, and 
bringing these fossils along with it. It must be observed, that in almost every 
instance they are surrounded by a coating of very fine coal of about one-half 
or three-fourths of an inch thick, having a polished surface with very little at- 
tachment to the surrounding matter. This I doubt not is the cause of the fall; 
the fossil dropping out sometimes as much as three feet in length, leaving a 
hole in the roof almostp erfectly circular. Often it falls in these large pieces, but 
sometimes the nature of the shale, of which its substance is composed, causes it 
to fall in portions of different thickness. It is to these falling pieces that the 
miner’s expressive term (kettle bottoms) applies. 
These fossil plants run from two to eight feet in circumference. The oc- 
currence of numerous impressions which you may observe in the specimens of 
parts of different plants in the shale, forming the substance of these fossils, is to 
me, I must confess, very difficult of explanation. Some years ago a friend of 
mine found a kettle bottom at Old Kenton colliery, eighteen inches in diameter, 
coated with fine coal, the substance of which was entirely mineral, carbon, or 
charcoal, with a mixture of earthy matter and pyrites. A portion of this speci- 
men is in the collection of the Geological Society. 
It is much to be regretted that hitherto none of these interesting fossils have 
been followed into the strata. We do not know how far they extend, or to what 
height they are standing. 
Again, in the coal districts of Scotland, amongst the troubles which affect 
the roofs of coal, there is one of a very singular form, known by the name of 
pot bottom or cauldron bottom, and are from the size of a foot to five feet in dia- 
meter. 
In working the bed of coal, the miner generally knows that he is approach- 
ing one of these, by the coal becoming twisted, and more difficult to work, and 
this continues till this trouble in the roof is passed. The general form is that of 
a cauldron with the brim dilated, the mouth of the pot being always inverted. 
The sides of it are generally lined with coalfrom one-eighth of an inch to an inch 
in thickness, and the pot or cavity is filled up with stone of the argillaceous. kind, 
or fire clay, having generally less mixture of sand than is in the roof stone around. 
The under surface of the stone which fills the pot is irregular and waving, not 
smooth like the roof adjoining. Although the coal which lines the pot is con- 
nected with the main bed of coal, it is of a texture altogether different, having a 
bright appearance like jet, and breaks into very minute cubical pieces. Some- 
times it has no bitumen in it, and is of the nature of glance coal. The sides of 
the pot are generally as smooth as glass, with small furrows or grooves in a verti- 
cal direction, so that there is very little tenacity between the sides of the pot and ~ 
the stone which fills it up ; this circumstance renders these troubles very danger- 
ous, particularly when they are of a large size, as they fall without giving any 
warning. ‘The peculiar singularity attending this trouble is the twisted texture 
and alteration which are found in the bed of coal immediately under and adjoin- 
ing it, witheut any mixture of the stone in it which fills up the pot. There is 
sometimes no lining of coal, and it generally happens that a piece of the stone 
which fills up the pot adheres to the upper part of the cavity, so that the trouble 
may go farther up into the strata than is emerged. This trouble requires to be 
mainutely investigated, and the pavement upon which the coal rests should be 
examined under the trouble, to ascertain if it is in any way altered in its structure, 
as is the case with the coal. Iam indebted to my much respected friend, Mr. 
Bald, for this latter information. Iam happy to say that it is his intention, at 
an early period, to devote his attention to these singularly curious objects,” 
