part 1] ECOLOGY OF COAL MEASTJEES OF GLAMORGAN. 33 



II. Ecology. 



The following ten charts (figs. 2-11, pp. 35-53) show for each 

 one of the ten seams : — 



(a) The proportion of the genera within each class. 



(b) The relative proportions of the various classes. 



The data upon which each chart is based are set forth in 

 corresponding Tables (I-X). These Tables show the distribution 

 of the different genera of plants within a class, giving the hori- 

 zon, locality, and number of blocks of shale in each alphabet, 

 Ai to Zi ; A2 to Z2 ; A^ to Z^ ; A* to Z* : also the total result 

 obtained in each class from A^ to Z^. Certain remarks on the 

 floral assemblages of each seam are appended (pp. 33, 54-57). 



The Five-Foot Seam (Table I & fig. 2, pp. 34-35) lies 

 immediately above the Millstone Gi-rit at the Britannic Colliery, 

 Grilfach Groch, and is the lowest seam found in this particular 

 area ; but at Clydach Vale another seam, known as the delli Deg, 

 occurs 30 feet below the Five-Foot Seam. The shales for exami- 

 nation were obtained in different directions from the shaft, that is, 

 south-south-west, north-north-west, and east, the maximum distance 

 in this area from south-south-west to east being 4000 yards. The 

 position of the shale-beds above the coal-seam varied from 3 to 

 15 feet. Layers of dark and grey shale were obtained from each 

 area. The dark shales always proved to be the more fossiliferous. 



Calamites dominated among the plants belonging to the Class 

 Equisetales. Not a single specimen of Sphenopliyllum was found. 

 Lycopodiales were almost absent. Among the ferns and fern like 

 plants, AletJiopteris was more numerous than any other genus, 

 except that in blocks A^-Z^, Neuro^oteris was the commonest 

 form. All other blocks, that is, A^-Z^, A^-Z^, and A^-Z*, showed 

 the predominance of Aletlio])teris. A significant fact here is the 

 predominance of this form, and then its sudden, almost complete 

 disappearance. It is only of rare occurrence in the overlying 

 horizons, 



Cordaite-leaves were found in great numbers, and were com- 

 monly associated with Calamites on the slabs of shale. No seeds 

 belonging to Corclaites were observed. 



Taking the different classes into consideration, plants belonging 

 to the Cordaitales were the dominant forms. Here again, it is 

 well to mention that this horizon alone yields Cordaitales in 

 greater number than plants of other classes. 



The Middle Yard Seam (Table II & fig." 3, pjD. 36-37) is 

 found in the shaft of the Britannic Colliery, 75 feet above the 

 Five-Foot Seam. Tlie shales for examination were obtained from 

 two positions, areas north-east and south-west, which are 2500 

 yards apart. 



The shales overlying the seam, for some 8 ito 10 feet in thicknesSj 



Q. J. a. S. No. 305. 3>. , 



