part 4] DISTKICT AROUND CORRIS A>"D ABERLLEFENNI. 



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The thickness of the Mottled Beds is about 30 to 35 feet, 

 although in some places in the Corris area they appear to be rather 

 thinner ; as, for instance, in Nant y Goedwig, in the unnamed 

 stream near the Vicarage, south of Corris, and between Corris 

 and Aberllefenni. In these localities they appear to be not more 

 than 20 feet thick ; but north-east of Aberllefenni they regain 

 their normal thickness. 



The Mottled Beds are overlain by rusty-weathering shales closely 

 similar to those exposed in the Machynlleth area, and they 

 doubtless correspond to the zone of Diplograptus acuminatus and 

 the JSLonogrnptus spp. Beds as defined in the latter area. 



They have not been examined in detail, and even fairly well- 

 preserved graptolites are difficult to extract. They are highly 

 cleaved : the cleavage-planes being practically vertical, while the 

 bedding-planes intersect the cleavage-planes at an acute angle. 

 In all their lithological characters they appear to be precisely 

 similar to the corresponding beds described farther south. 



From the old quarries in these beds at Taren y Gesail the 

 following graptolites have been obtained : — 



Petalograptus palmeus (Barrande). 



CUmacograptus scalaris (Hising-er) 



sennit lato. 

 CUmacograptus tomquisti Elles & 



Wood. 

 Glyptograptus tamariscus Nicholson. 

 Orthograptus mutabilis Elles & 



Wood. 



From ISTant y Goedwig : — 



CUmacograptus tomquisti Elles & 



Wood. 

 Glyptograptus tamariscus Nicholson. 

 Monograptus acinaces Tornquist. 



From the old quarry in the Dulas Yalley immediately north-east 

 of ('orris : — 



Dimorplwgraptus confertus 



sivanstoni (Lapworth). 

 Monograptus communis (Lapworth). 

 M. concinnus (?) Lapworth. 

 M. acinaces Tornquist. 

 M. triangulatus (Harkness). 



Monograptus regularis Tornquist. 

 M. sandersoni Lapworth. 

 M. triangulatus (Harkness). 



CUmacograptus scalaris (Hisinger) 



sensu lato. 

 Monograptus concinnus (?) Lapworth. 



Monograptus acinaces Tornquist. 

 Orthograptus mutabilis Elles & 

 Wood. 



From Nant Llwydiarth near Cymerau, north-east of Aberlle- 

 fenni : — 



CUmacograptus hugh'esi (Nicholson). 

 CUmacograptus scalaris var. nor- 



malis Lapworth. 

 CUmacograptus tomquisti Elles & 



Wood'. 



GVyptograptus tamariscus Nicholson. 

 Monograptus atavus Jones. 

 M. communis (Lapworth). 

 M. rum munis var. rust ruins Elles & 

 Wood. 



Monograptus concinnus (?) Lapworth. 

 M. cyphus Lapworth. 

 M. fimbriatus (Nicholson). 

 M. gemmatus (Barrande). 

 M. gregarius Lapworth. 

 M. incommoclus (?) Tornquist. 

 M. raitzhainiensis (Eisel). 

 M. revolutus var. austerus Torn- 

 quist. 

 M. sandersoni Lapworth. 

 M. triangulatus (Harkness). 



The thickness of the Cwmere Group is about 300 to 350 feet. 



