276 MISS G. L. ELLES AND MISS E. M. E. WOOD ON THE [May 1 896, 



III. Genekal Sequence. 



In this area we believe that we have a succession of graptolitic 

 mudstones representing beds of Llandovery, Tarannon, and Wenlock 

 ages, and we hope to show that the omission of Llandovery Beds in 

 the Conway succession of the earlier surveyors was erroneous. "We 

 consider that the general sequence in descending order is as 

 follows ; — 



5. Denbighshire Grits and Flags. 



4. Wenlock Shales. 



3. Tarannon Shales. 



2. Upper Llandovery Beds. 



1. Bala Beds. 



The junction between the Bala and Llandovery rocks is nowhere 

 visible. The former do not come to the surface south of the 

 Afon Gyffin, but at the time of our first visit drainage-operations 

 were in progress along the road passing the timber-yard on the way 

 to Benarth, and at a few feet below the level of the road black 

 graptolitic shales containing Diplograptus foliaceus (Murch.) and 

 Climacograptus licornls (Hall) were seen, apparently in situ, under- 

 lying the Tarannon Shales. If this be really the case, the Lower 

 Tarannon rests uneonformably on rocks of Bala Limestone age, and 

 the succession is here different from that seen on the other side of 

 the fault (F. 2 in map, p. 274), where Llandovery rocks occur, but 

 it is unlikely that the Birkhill Shales have been overlapped in this 

 short distance. 



Since there is no junction visible between the Bala and Llan- 

 dovery rocks, we are unable to determine definitely whether the 

 Lower Llandovery rocks are absent or not in the district. 



Note on the Bala Rocks of the Conway District. — On the other side 

 of the Biver Conway, in a quarry of Bala rocks on the hill above 

 Deganway, we have found remains of several large trilobites. Many 

 seem referable to the species Phacops appendiculatus (Salt.) ( = P. eu- 

 centra, Ang. ?). This would tend to show that we have here repre- 

 sentatives of the Ashgill Shale fauna of the Lake District. If this 

 be the case, there exists in this part of North Wales a higher series 

 of Ordovician rocks than has hitherto been supposed, and hence the 

 break between Ordovician and Silurian rocks is less than was formerly 

 believed to be the case. 



The Upper Llandovery rocks pass up conformably into the 

 Tarannons ; but on palseontological grounds we believe that the 

 latter are overlapped by the Wenlock Shales, and that the highest beds 

 — that is, the zone of Cyrtograptus GVayce (Lapw.) — are not present 

 here. 



The best section of the Wenlock Shales is to be seen on the shore 

 below Benarth, and here we approximately determined the upper 

 limit of these beds, on lithological grounds, at a point where the 

 beds become more flaggy in character and contain bands of grit. 



The exposures on the side of the hill were not sufficiently good to 

 enable us to determine the upward limit with certainty. 



