280 



J. E. MAER ON THE CAMBRIAN AND 



Another remarkable instance is seen in the Eraehiopod Le^tcena 

 quinquecostata, which is found in the limestone of Bala, but in the 

 Lake district has not been certainly found lower than the beds in- 

 tercalated with the Graptolitic mudstones, where it is abundant ; it 

 occurs there also in the middle and upper Cold well beds. 



Section in the Neighbourhood of the Rectory, Oerrigydrudion, 

 (Length of Section about i mile.) 



8. 





N. 



E.S.E 





>> 



Quarry, 200 



yards S. of 



1 



I'ynyi 



hydd. 



« 

 J^ 



8. 10° W.. 

 W.N.W. 



-N. 10" E. 



Millpond. 



a. Grey Bala Shales. 



b. Undulating series of calcareous grey grits, false-bedded and ripple-marked , 



with many clay-galls. (Near the top of these are blackish-grey cleared 

 bands, as at *.) The whole of b is probably the equivalent of the Corwen 

 Grits, and passes up into <?• 



c. Leaden-black, cleaved, pyritous shales, with many Graptolite3=Graptolitic 



Mudstones. d. Pale-green cleaved shales =Tarannon Shales. 



4. The Upper Bala Beds. 



It is somewhat diflS.cult to know which of the Dee-valley beds 

 should be included under this head. The Hirnant Limestone is 

 placed hereby Salter and others (see Cat. Cambr. & Sil. Foss. Woodw. 

 Mus. p. 72) ; and it is characterized by Orihis hirnantensis, stated 

 by Davidson (in his ' Monograph of Palaeozoic Brachiopoda ') to be 

 undistinguishable from Strophomena siluriana, the characteristic 

 Brachiopod of the Ashgill Shales, which are also placed on this 

 horizon. 



There is also a calcareous grit, from which I obtained Echino- 

 sphcerites Davisii^ just below the pale shales by the roadside about 

 i mile S.W. of Maeshir, which is probably to be referred to this series. 



Neither of these beds shows much correspondence in lithological 

 character with the Ashgill Shales ; there is one locality, however, 

 where the beds do bear a strong lithological resemblance to these 

 shales, viz. the shales with Orthis alternata, seen by the roadside, one 

 mile south of Cerrigydrudion. Besides abundance of Orthis alternata, 

 they contain Crinoid stems, Beyrichia, and Lingula ; and in them is 

 seen an ash bed*. They occur not very far from the outcrop o£ 



* [Eock 1 mile S. of Cerrigydrudion. A rock probably of pyroclastic oi'igin, 

 but so much altered by pressure and subsequent chemical change that it is 

 difficult to form an opinion. Certainly many of the fragments are of igneous 

 origin. The felspar is much decomposed, and various secondary products are 

 abundant. All that it would be safe to say is that the fragments do not belong 

 to the more acid group of lavas, probably they are andesitic ; but seeing that 

 the rock has been much altered, they might be yet more basic. (If the rock is 

 rich in carbonate, the latter is probably the case.) — T. G. B.] 



