part 2] PALEOZOIC eocks of the llangollen district. 195 

 And the following from the farmyard at Hafod-yr-Abad : — 



Monograptus runcinatus Lapworth. 

 M. nudus Lapworth. 

 If. exiguus Nicholson. 

 M. turriculatios Barrande. 



Monograptus pandus Lapworth. 

 M. nodifer Tornqiiist. 

 If. priodon Bronn. 



This assemblage indicated a low position in the M.-crispus 

 Zone. 



The deposits overlying the M.-crispus Zone may represent the 

 griestonensis beds, and are interesting on account of their occa- 

 sional trilobite and brachiopod remains. In the steep lane heading 

 from the old Ruthin road to Pentre-uchaf, half-a-mile south of 

 Bryn-yr-Odyn, the following forms were collected : — 



Favosites sp. 



Orthis (BiloMtesJ hiloha Linnasus. 



Phacops cf. elegans Sars & Bceck. 



Phacops stolcesi Milne-Edwards. 

 Phacops sp. 



The M.-crenulatus Zone is characterized by its peculiar lithology 

 (dark slates and mudstones), which easily distinguishes it from the 

 pale slates below, and the banded and laminated mudstones and 

 slates of the overlying Wenlock. It occupies, as a result of gentle 

 folding, a wide strij) of country near the Moel-y-faen quarries. 



The following forms were found at a point 300 j^ards north of 

 Fron-adda on the side of the old Ruthin road : — 



Monograptus griestonensis Nicol. 

 Jf. vomeriniis Nicholson, var. 

 crenulatus Tornqnist. 



Retiolites fGladiograptusJ geinitzi- 

 anus Barrande var. angustidens 

 Elles & Wood ; 



while, on the old tram-line 340 yards north-west of Fron-adda, an 

 abundance of M. vomeriniis var. crenulatus is found. TJiis out- 

 crop appears to be part of a faulted inlier. 



The Myiiydd-Cricor Area. 



In this district the Yalentian, as a rule, dips outwards from 

 Mynydd-Cricor in conformity with the anticlinal structure, but it 

 is much affected by faults. Near Ffynnon-Tudur there is also 

 considerable thrusting, and the general dip is reversed in the 

 Tarannon Beds that override the Lower Valentian Series, so that 

 Wenlock Beds lie against the Ordovician on the West side of Cricor. 



Lower Valentian. — The Lower Yalentian rocks of M3mydd- 

 Cricor exhibit the typical speckled and pale grey-green aspect, and 

 are rarely fossiliferous. The following forms were collected from 

 Bryn-Rhedyn, 1 mile east by south of Cricor Farm : — Flecfam- 

 honites scissa Salter and '^ Strophomena o,^. fletclieri Davidson. 



The summit of the Lower Series appears to be in the zone of 

 il£ cypfhus, for the following forms occur, within a few feet of 

 typical Tarannon mudstone in the ravine, half a mile south-east 



o2 



