Vol. 67.] ASSOCIATED ROCKS OP NORTH-EAST MONTGOMERYSHIRE. 433 



between 20 and 30 feet of massive red quartzose conglomerate 

 merges upwards into red sandy flagstones. The beds are very- 

 ferruginous, and contain large quartz-pebbles, green jaspers,, 

 fragments derived from the lower beds in the sequence, as well 

 as pebbles of fine-grained igneous rocks of unknown origin. This 

 conglomerate has been largely quarried for building-stone and 

 road-metal, but it is now superseded by the rock from the Welsh- 

 pool Dyke, and the upper calcareous beds of the Gaerfawr Series. 

 At Cloddiau the group rests on a still higher horizon of the 

 Caradocian rocks. The Lower Gaerfawr Grits crop out from 

 under the conglomerate in Harriets Hill on the south ; while on the 

 north, higher beds still emerge in Moel-y-garth. The Conglomerate 

 itself thins out as it is traced towards Y Frochas, where it loses 

 its red coloration, and becomes a yellow grit resembling the Mill- 

 stone Grit. The series ends abruptly here against a fault, and, 

 owing partly to the thinning-out of the beds over the anticline, 

 and partly to the overlap of the Ludlow Shales, it is not seen again 

 between Y Frochas and Welshpool. 



At Cloddiau the beds run north-westwards, resting against the 

 western flanks of Moel-y-Garth, until they terminate against the 

 Moel-y-garth Fault. Some faulting parallel and subsidiary to that 

 fault disturbs them in places. At the place marked ' Laundry ' 

 on the map (PI. XXXIII) they are overlain by about 40 feet 

 of a grit which weathers in a peculiar manner. The unweathered 

 grit is hard, blue, and calcareous, and runs in massive beds 6 to 

 10 feet thick, with wayboards of shale. When weathered, this 

 grit becomes soft, crumbly, and chocolate-coloured, and it is only 

 then that it reveals the fact that it is fossiliferous. The strata 

 have evidently been disturbed, since the shale-bands between the 

 grits are crumpled and broken in a complex manner. 



On the western side of the Moel-y-garth Fault the beds come in 

 again at Groes-lwvd, and can be traced by Cross Wood to Trawscoed 

 Hall, where they appear to thicken very greatly and form a wide 

 outcrop. The apparent increase in thickness is due to gentle 

 folding in the strata. 



It will now he evident that this Conglomerate Series, which 

 rests in turn upon every member of the Ordovician sequence, forms 

 an excellent natural base to the Silurian strata of the district. 



(2a) Cloddiau Group. — Above the Red Conglomerate Series 

 from Cloddiau to the Laundry, there is exposed, chiefly in the road- 

 side and in the stream-section which runs parallel to the road, a 

 series consisting of 20 to 30 feet of blue shales overlain by about 

 200 feet of soft, sandy mudstones, with some siliceous flaggy 

 bands. The beds are very fossiliferous in places, and were considered 

 by Bickerton Morgan to be of Lower Wenlock age. The fossils 

 obtained from them, however, proved them to be distinctly of 

 Llandovery age. They are not well exposed, and appear to be quite 

 barren in places. The fossils obtained near the Laundry would 

 seem to indicate the presence of zones of both the Lower and the 

 Upper Llandovery. 



