FORMATION OF COAL. I97 



inclined to think that in some species at any rate they did not. 

 The ribs are generally, marked by scars of an oval or round shape 

 having in the centre other small scars 3 these appear to me to 

 present a tubical appearance when covered by bark. 



The Lepidodendra are very similar to the last, but instead of 

 being marked by flutings, the vascular woody cylinder was 

 covered with a more or less hexagonal shaped scars. From these 

 foliage was given oflF ; but as the branches grew this appears ta 

 have dropped off, being confined only to the twigs, or rather their 

 equivalents. A short time ago there was found in the roof of the- 

 ''Two Foot " seam. Speedwell Pit, near Bristol, a very fine stem 

 about six feet long with fructifications, all complete. A more 

 perfect specimen I never saw, but the main branch was quite 

 devoid of foliage, while those radiating off were covered, especially 

 near the extremities, at which there was also a fruit. 



I have now given an outline of the chief tree plants which 

 flourished during the great Carboniferous age, there are many 

 others as well as ferns which might be named, but it is needless in 

 this paper to do so, and I will only add that they were mostly, if not 

 all, flowerless. 



The Climate. Coal is to be found in almost all parts of the 

 world, including the Arctic regions ; it is therefore obvious that 

 the climates of the world must have great changes. Upon 

 this point there is no doubt, as we have other instances of change 

 of climate notably in the glacial epochs. 



Several theories have been advanced to account for change of 

 climate. One which formerly gained much credence, attributed it 

 to the radiation of internal heat into space by which the earth has 

 become gradually cooled ^down, in which case the older formations 

 would have been warmer than the later ones. 



It was again suggested that the change was due to an alteration 

 in the position of the earth's^axis, caused by the elevation of land 

 between the poles and equator. 



The theory adopted by the late Sir Chas. Lyell has gained 



