THE GABBONIFKBOUS SYSTK.M '2'>\ 



Phillipsia pustulosa, Griffithides globiceps, Brachy- 



metopus ouralicus. 

 Entomostraca. Leperditia Okeni. 

 Pisces. Eurynotus crenatus, Rhizodus Hibberti, Elonichthys 



Kobisoni, Cladodus striatus, Cochliodus contortus, 



Orodus ramosus, Petalodus acumiuatus, Psaramodus 



rugosus. 



B. BRITISH AVONIAN STRATA 



The surface areas occupied by the Lower Carboniferous or 

 Avonian Series in the British Isles are shown on most geological 

 in.-!])*. They are clearly shown on the cheap (2s.) Index map of 

 the Geological Survey, and most of them are indicated in the maps 

 (Figs. 87 and 94) of this volume. The large extent of the area 

 which they occupy in Ireland is especially noticeable, though the 

 student must remember that in Fig. 94 the superjacent Coal- 

 measures are not shown. 



In England it is probable that the limestones extend eastward 

 under large parts of the southern and central counties, but they 

 do not appear to exist in the East Anglian counties, where many 

 borings have been made at different times, but have always found 

 rocks of pre-Carboniferous age beneath the cover of Cretaceous 

 strata. 



With regard to the superposition and relation to the older rocks 

 it may be stated generally that the Carboniferous strata follow 

 those of the Upper Devonian or Upper Old Red Sandstone in 

 conformable succession wherever the latter are present ; but when 

 these are absent, the Carboniferous rests unconformably upon the 

 older formations. 



With respect to the subdivisions of the Avonian Series recent 

 studies by Dr. Vaughan, Dr. W. Hind, and Professor Garwood have 

 shown that it is everywhere divisible into two stages, and as 

 French geologists had already made two similar divisions, their 

 names have been adopted, namely Tournaisian for the lower and 

 Visfon for the upper stage. In England each stage appears to be 

 divisible into three zones, but the delimitation of these zones has 

 not yet been determined in all districts. Where fully developed, 

 the normal succession is as follows : 



f Dy. Cyathaxouia sub-zone. 

 i-{ D. Dibunophylluni zoue. 

 I S. Seminula zone. 



Visdan-i D. Dibunor 



C. Syringothyris zone. 

 Tournaisian-j Z. Zaphreutis zone. 

 [ K. Cleistopora zone. 



