520 Notices of Memoirs — British Association — 



area. The Bala Limestone is not developed as a calcareous bed in 

 the northern part of the area, but is somewhat more persistent as 

 a definite band in the southern and eastern portions of the district. 

 The true relations of these horizons to each other is seen in the 

 type section at Gelli Grin, where the Bala Limestone at its maximum 

 thickness is overlain by light-coloured, pasty niudstones containing 

 a typical Rhiwlas Limestone fauna. The i'auna is not nearly so 

 rich in individuals as that of the Ehiwlas Limestone itself, but all 

 the more important genera and species seem to be represented. 

 Confirmatory sections are also seen east of the fault near Gelli Grin 

 Farm, and also on Bryn Cut. 



5. The Shelly and Geaptolitic Paunas of the British 



Oedovician. By Dr. Geetrude L. Elles. 



rpHERE are two main types of 'shelly' faunas of Ordovician age 



1 in the British Isles, and each of these can be further subdivided 



into a number of sub-faunas which can be correlated by reference to 



associated graptolite-bearing beds. 



Ordovician Faunas. 



The main shelly types may be described as — 



A. Asaphid-Trinucleid-Calymenid fauna. 



B. Cheirurid-Lichad-Encrinurid fauna. 



