586 W. W, WATTS ON THE IGNEOrS AND 



the ashes. Some bosses of rock on Moel-y-Golfa may be intrusive, 

 but I have found no conclusive evidence of this ; most of them are 

 certainly lavas and have suffered denudation to form the conglome- 

 rates. 



IV. SiLUEiAN EocKs (SeclgwicJc). 



These occupy an area S.E. of the ridges, and closely overlap the 

 Cambrian rocks, particularly on the flank of Middletown Hill, where 

 the lowest beds are exposed. It is extremely unfortunate that, 

 though these rocks are in close proximity to exposures of the volcanic 

 conglomerate, the actual base and the character of the junction cannot 

 be determined. The lower rocks, exposed in a lane leading from 

 Middletown to the Barytes mine, consist of greenish-brown, rather 

 tough, thin-bedded mudstones, and soft sandstone much stained with 

 ochre and containing a few quartz pebbles and some hardened, 

 impure siliceous concretions and beds ; they are barren for the most 

 part, but have yielded a few shell-casts. The strata dip at 35° S. 

 30° E., and about 250 feet are exposed. I have found the following 

 fossils, most of which Dr. Davidson has kindly examined for me : — 



Pentamerus glohosus ?, Sow. 



oblongus, Sow. 



undatus, Sow. 



Athyris ? sp. 



Orthis rustica?, Sow. 



—r-> sp. 



Leptaena transversalis, Wahl. 



Strophomena rhomboidalis, Wahl, 



together with a Gasteropod and a small Brachiopod of an unknown 

 genus, but resembling Trijplesia. These fix the age of these beds as 

 May-Hill, and so there must be a marked break between the Cam- 

 brian and Pentamerus-beds, and an unconformability of which the 

 slight change in dip gives little evidence. 



Faults which bear barytes traverse Middletown Hill to the N.E. 

 of this exposure, coursing ^. 35° W. and S. 35° E., and introduce a 

 slip of similar rocks between the Cambrian rocks. In this strip I 

 have found : — 



Petraia subduplicata ?, M'Coy. 



Pentamerus oblongus, Sow. 



There are no exposures to show what immediately follows these 

 beds, but the next rock seen is a purple shale, shown in the small 

 brooks near Middletown Schoolhouse and the New Inn, and in the 

 brook which rises near the Pour Crosses Inn. It is a purple shale, 

 soft and micaceous, containing green bands and concretions. N"o 

 fossils have hitherto been found in it. It dips S. 10° E. at from 

 35° to 50°, and appears to be about 200 feet thick, while the total 

 thickness from the lowest May-Hill beds exposed to the top of this 

 shale cannot be much less than 660 feet. • The upper part becomes 

 greyer and more concretionary till it passes into the ordinary grey 

 Wenlock shale. The purple beds have also been recognized along 

 the brooks and roads around the Buttington inlier, but I have not 

 yet recognized Pentamerus-beds there. The position, appearance, 

 and character of these shales link them with the purple shales above 



