484 ME. 0. X. JONES ON THE HAETFELL-VALENTIAN [Nov. I9O9, 



folded and broken, there can be no doubt as to their original 

 order of superposition. Furthermore, graptolites occur in abundance 

 and in exceptionally good preservation, and the general absence of 

 cleavage renders their extraction easy. 



On a broad view, the structure of the gorge resolves itself into 

 a faulted anticline, east of which is a shallow syncline. As the 

 gorge winds backwards and forwards across the strike, it follows 

 that the same strata are exposed in several parts of the river-bed : 

 and, for this reason, it is a little difficult to choose a starting- 

 point for the description of the section. As it seems desirable 

 to deal with the rocks as far as possible in ascending order, I shall 

 commence with that part of the gorge where the lowest beds are 

 exposed. This lies at the bend of the river 500 yards south-south- 

 east of the bridge, and a little below the end of the plantation which 

 skirts the south side of the gorge from near the Gogerddan Arms 

 Hotel. On the east side of the river are some hard sandy flags 

 with shales yielding Cephalograptus (?) acuminatus and Clima- 

 ■cograptus scalaris var. normalis. Near the centre of the river- 

 bed the strata are violently contorted, and I only found a single 

 specimen of Glimacograptus medius. When the river is low, it 

 flows close to the western bank along a fault-line which throws 

 •down somewhat higher strata on the west. These consist of flags 

 and shales, with three gritty bands which stand out prominently 

 in the bed of the river. The lowest is a tough grit, which is 

 truncated by the strike-fault and jammed against the older bedi 

 on the east. The middle band is made up of alternations of flags 

 and shales, and beds of hard blue grit with cubes of pyrite. The 

 highest band, which is also the thickest, consists of massive grits, 

 gritty mudstones, and flags, the whole being about 18 feet thick. 

 This band enters the southern bank of the gorge exactly opposite 

 the end of the plantation, but reappears in the river-bed about 

 170 yards to the south. A few yards below it is a similar band, 

 which may be a repetition of the first by a strike-fault ; but it 

 is more likely that it corresponds with the middle band seen 

 higher up the river, although the thickness of beds between them 

 does not quite match in the two places. 



The strata succeeding the highest band are completely exposed 

 between its outcrop and the next bend of the llheidol, where a small 

 tributary enters from the west. Their lower part consists of flags 

 and shales ; but the proportion of shaly material so increases in 

 ascending the section that near the bend shales predominate. They 

 weather to a pale yellow as a rule ; and their surfaces are some- 

 times minutely pitted, owing to the removal of globules of pyrite. 

 In the lower beds Climacograptus scalaris var. normalis was almost 

 the only fossil found ; but in the higher and more shaly beds Mono- 

 graptus atavus, sp. nov. occurred frequently along with it. The dip 

 in this part of the river is due west ; but close to the bend the strata 

 are folded into a sharp syncline followed on the west by an equally 

 sharp anticline, the axes of which are only about 15 yards apart 



