38 



gradually diniiiiisliiug as we come eastward (away from the centre of dis- 

 turbance), and dicing out altogether as we approach the East Crop, near 

 Rhymney, where the coals become eutii-ely bituminous. Now, geologists are 

 very much divided as to the cause of anthracite or stone coal. Some say that 

 the cause is chemical, and is still going on ; but to this my answer is, — Why 

 should not the chemical agency be exerted over the whole of the field, instead 

 of gradually decreasing in the way that the anthracitio tendency does ? and, 

 moreover, in the very districts of Cannarthenshire and Pembrokeshire, where 

 the anthracitic character is strongest in the Lower Measures, tlie Upper Measure 

 Coals within two or three miles distance, are entirely bituminous. If it was a 

 chemical force still going on, how is it that force does not alter the Upper 

 Measures in the very same area as the Lower Measures ? We find that this 

 same force had an equal effect in the other direction, viz., in Ireland, the coals 

 in the Kilkenny Basin being equally anthracitic with those of Pembrokeshire. 

 Does not this bear out the theory of a central and radiating disturbance ? 



Whatever might have been the cause of this distui-bance (and I am of 

 opinion that it was one of Plutonic agency), it seems to me that it took place 

 after the deposition of the Lower Measures, and before the deposition of the 

 Upper Measures, the character of which was consequently left untouched. 



Another consequence of this force was not only to alter the configuration 

 of the basin interiorly and the character of the coals, but also to cause lesions or 

 fractures in the coals themselves. The results of those fractures were large 

 "faults," which we find running down and parallel with nearly every valley, as 

 though the formation of the valley and the fault were synchronous. These 

 faults contribute much to the main drainage of the valley, afterwards deepened 

 by the action of the surface rivers. 



4. — The next great era was the deposit of the Upper Measures, which, 

 wherever they are found, seem to be but little or not at all affected by the main 

 or big faults of the Lower Measures. 



5. — Then there ensued a gradual elevation of the whole basin, the effects 

 of which we see in the parallel terraces, or sea beaches on the hills of the North 

 Crop, each terrace marking a period of rest when the waves of the Permian 

 sea washed the bases of the Coal measure hills. 



6. — The last and perhaps most important change was denudation, which 

 has left the Coalfield mainly as it is now. The extent of this denudation may 

 be imagined when I tell you that Professor Ramsay estimated that 9000 feet 

 of Upper Coal Measures have been carried away, and that from the very district 

 on which we stand the whole of the Upper Measures have been swept away, with 

 the exception of a small area of coal which is called the Mynyddwslyn vein, 

 and which supplies the house coal of Newport and Cardiff. This little patch, 

 which is now nearly worked out, represents in the eastern portion of the field 

 thia 9000 feet of Upper Measures. But westward beyond the Bhoudda-valley, 



