434 Mr. R. C. Taylor on part of the Mineral Basin 



streams which these Cicms, or deep ravines^ contain, have a progressively 

 diminishing- inclination as they proceed from their sources. We have shown 

 the profiles of three of these mountain rivers, noting the fall in feet per mile 

 in the respective divisions of each. 



Nant Ddu Brook, subdivided into five portions or lengths. 



1st or upper portion, has an average inclination of 1040 feet per mile for 5 mile. 



2nd portion 450 -5 mile. 



3rd 275 ^ mile. 



4th 240 ^ mile. 



5th, to its junction with the Afon Lhvyd, falls only 110 1 mile. 



Bwrgwm Brook. 



1st, or upper half mile, descends on a plane of 800 feet in a mile. 



2nd, second half mile G60 feet per mile. 



3rd, three fourths of a inile to the Afon .... 230 feet per mile. 



Sychan Brook, in three portions. 



1st. — \ of a mile from its source, descends with a fall of 650 feet per mile. 



2nd. — I of a mile at the rate of 444 feet per mile. 



3rd. — \ of a mile to its junction with the Afon, only .... 230 feet per mile. 

 The Afon for the succeeding mile proceeds with an inclination of 90 feet only. 



Inclination of Strata. — The prevailing dip is about 3 inches' fall in each 

 yard, or from 400 to 450 feet per mile. At Abersychan and Verteg the 

 direction of the dip is nearly west by compass, and consequently the level 

 course is not far from north and south. 



Faults. — These of course have been but partially explored in a district 

 which has only been recently penetrated by mining operations. We have 

 traced upon the model the direction of one which was encountered at an 

 early stage of the works at Abersychan, and passes for an unknown di- 

 stance along the bottom of the Sychan Valley. A level which was con- 

 ducted along a coal vein suddenly passed into a bed of iron mine, whose proper 

 position was 50 feet above the coal ; and thus, for a time, the same level 

 served on one side of the fault for working coal, and on the other, through this 

 change of position, for working the iron ore*. 



At Pontnewynydd, and passing upwards in the direction of Nant Ddu 

 Brook, a considerable fault appears, by which all the strata in the promontory 

 called Pen ij Tranch are brought down, and probably are thrust forward in a 

 mass, somewhat beyond the eastern boundary of the coal field, perhaps more 

 than 300 feet below their proper position. On the south, or opposite side of 



* The direction of the fault is shown on the model, but not the nature of the disturbance. See 

 also the Map, PI. XLII. 



