602 FAUNAL SUCCESSION OF THE UPPER BERNICIAN 



This phenomenon is to some extent exhibited in certain 

 specimens of the simple form of Cyath. regiiwi from D2 of the 

 Avonian. The reduction in size and the conical form of the 

 simple coral is an intimation of approaching inimical con- 

 ditions. 



The IVb and IVc fauna is probably the moribund repre- 

 sentative of the Avonian coral fauna vi^hich reaches its acme 

 in IVa. 



The following correlation of the Bernician vi'ith the Dibuno- 

 phyllum Zone of the South-West Province seems the most 

 probable : — 



Northumberland 



South-West Province 



Millstone Grit, 



Millstone Grit. 



rIVc. 



Dy -]lVb. 



(IVa. 



D2-3. 



III. 



II. 



D2. 



I. 



Di. 



a. 



Concretionary beds at 

 top of S2 ? 



N.B. — No attempt has been made in the above table to 

 indicate the relative thickness of the various horizons. 



VI. 



THE BERNICIAN LIMESTONES, THEIR GEOGRAPHICAL 



DISTRIBUTION, STRATIGRAPHICAL CHARACTERS 



AND FAUNAL CONTENTS. 



The Redesdale Ironstone Shale, Redesdale Lime- 

 stone and Fourlaws Limestone. 



Geographical Distrihition. 



These limestones are the most northerly of those running 

 parallel to the Tyne. They cross the North Tyne south of 



