86 
streams and water torrents as at the present day. Once in the 
water the rate of decay would depend upon the nature of the 
debris in suspension and solution. The inner parts of the tree, 
with the outer bark, being more liable to decay than the epider- 
mal layer, a cylinder would result, into which it may be naturally 
assumed the sediment would accumulate. The weight of this 
accumulation would, in time, cause the cylinder to sink, and this 
coming to rest in coal forming vegetation would result in a 
coalstone. Or it may be that the plants decayed and were filled, 
as described, while standing. 
The question may be asked would the coal period trees deuee 
as we say; a quotation from Professor Wiiu1amson, of Man- 
chester, taken from his works on the classification of coal 
plants will go a long way to confirm what we have suggested. 
He says “It is the bast layer with its investment of thick 
walled epidermal cells which has furnished in nearly every case 
the carboniferous film that covers the stem of the Lepidoden- 
droid plants so abundant in the shales and sandstones of the 
coal measures. The bast layer evidently gave to the bark the 
faculty of resisting the decay which so effectually cleared out 
all the more central tissue. It was the double layer that 
constituted the cylinder, the two sides of which were brought 
together and flattened by superimposed pressure when the stems 
were prostrated and which constituted the hollow mould into 
which mud and sand were poured when they remained standing.” 
A few feet above the lower series Great Vein there is a bed 
containing large ironstone nodules, some of which are tolerably 
rich. These have much the same origin as coalstones. The 
only difference between them is, that the water in which they 
were immersed contained in the case of the iron nodules, a 
larger proportion of iron; this rapidly attacked the parts most 
liable to decay, with the formation of carbonate of iron, and, 
with a proportion of Silica and other substances filled up the 
cylinder thus formed. The shape and the well-preserved 
markings on these stones is very suggestive of their origin. 
In the ironstones the markings chiefly indicate branches and 
trunks of trees; with the coalstones Stigmarie predominate. 
