C— GEOLOGY. 55 



the parent trees. That they were di'ifted into place and distributed 

 with the thinness and regularity which we see the layers to possess is 

 quite inconceivable. For sometimes a layer of spore coal an inch in 

 thickness may 'be traced at a specific level in a seam over an area of 

 scores of square miles. In the Haigh Moor seam there is a layer of 

 this kind half or three-quarters of an inch in thickness, which can be 

 traced through several collieries in the neighbourhood of Castleford. 



The constituents of fusain, or ' mother of coal,' are even more easily 

 recognised than those of spore coal. Upon a bedding plane fusain is 

 seen to be composed of fragments of plant-tissue, commonly showing 

 a fibrous or cellular structure, and in many instances of rectangular 

 form suggesting scraps of wood. In the seams most commonly used 

 as house-coal in Yorkshire recognisable fragments of Calamite stems 

 are very common — usually in single internodes or lesser fragments, 

 though occasional examples of three or four internodes in apposition 

 are found. Some fusain, according to White, is composed of fern 

 leaves. 



The charcoal-like aspect is in agreement with the i-esults of chemical 

 analysis, which show a very high carbon content. 



Eusain layers are much less defined in the spore coal than in soft 

 coal, a fact which may have some bearing upon the mode of origin of 

 the two materials. In bright coal the fusain layers exhibit consider- 

 able regularity and continuity. 



There has been much speculation regarding the origin of fusain 

 layers, some authors ascribing them to the wood and smaller plant 

 rubbish which appear to have undergone rapid aerial decay at or near 

 the water surface of the swamp in which most of the debris was 

 submerged. 



This explanation appears to me the most in accord with the facts 

 as I have observed them, but the regularity of the layer seems too great 

 and the fusainisation too indiscriminate and too complete to accord with 

 any supposition that these layers represent the ordinary crop of decay- 

 ing materials. It would be worth a detailed and systematic study to 

 ascertain whether they represent the raffle of dead twigs, leaves, and 

 other stuff brought down by periodic flood-waters. This supposition 

 gains a little support in my experience of the abundance of calamitean 

 stems, for although Calnmites is provided with a stout woody axis, 

 the cortex has very large air-spaces that would impart great buoyance 

 to the fragments. I have collected the drift along the flood-line of 

 two English lakes, Bassenthwaite and Semmer Water, and in both 

 cases fragments of Kquisetiini were preponderant elements. Periodic 

 flooding is not inconsistent with what is known about the conditions of 

 coal-formation, or of the regime of gi'eat rivers. The great swamps 

 of the world are in the flat portions of the course of great rivers or in 

 their actual delta. The North Sea, for instance, we have chosen for 

 example, was a great deltaic flat. Tliat the Coal Measures wei-e a 

 similar deltaic flat is evident. 



The idea that fusain is the imperfectly burnt residue of a forest fire 

 is opposed by so great an array of facts that it is difficult to understand 

 its frequent restatement. The fusain layers are as even and regular 



