\ ol. 60.] RH.ETIC OF THE SOUTH-WALES DTRECT LINE. 199 



Cotiiam Marble (or its equivalent). 





V. Shales, with usually a thin limestone-band containing ostracods 

 (Da nv inula) and not infrequently Estheria and insects. 



IV. Shales and ai-gillaceous limestone (usually nodular or concretionary) 

 containing the maximum of Estheria minuta, var. Brodieana. 

 This is the horizon at which Naiadita is abundant. 



/III. Dark shales (usually with one or more very hard beds of dark 

 limestone), containing the maximum of Pecten valoniensis. 





II. Black shale (with occasional thin sandy bands), containing the 

 ? i; ■< maximum of Avicula contorta, and probably also of Schizodus 



i_] -^ j Ewaldi and Myophoria postera. 



I. Non-fissile black shale, with few fossils. Beds poor in mollusca, 

 ^ but frequently teeming with vertebrate remains. 



The notation here adopted may be approximately correlated with 

 that employed by the late Edward Wilson and Mr. L. Richardson, 

 as follows : — 



V includes beds in the neighbourhood of 1 of Richardson and m of Wilson. 

 IV ,, ,, ., 3 of Richardson and k of Wilson. 



Ill „ ,, ,, 7 of Richardson and g of Wilson. 



II „ „ „ 8 to 12 of Richardson and d of Wilson. 



I ,, ,, ,, 15 of Richardson and a of Wilson. 



A closer correlation seems neither practicable nor desirable, and 

 all attempts made to find the exact equivalent in a distant locality 

 of each thin hard layer appears to us, from the very nature of the 

 deposits, to be doomed to certain failure. 



If. instead of considering maxima, we regard entire ranges, it 

 would be impossible to maintain even the small number of divisions 

 that we have adopted in this paper. For example: — 



Ostracods are found throughout IV as well as in V. 



Estherice are found in V as well as in IV. 



Pecten valoniensis is found quite commonly in most localities 

 associated with Avicula contorta and Schizodus Ewaldi : in fact, the 

 Lilliput section is almost unique in the rarity with which this 

 association takes place (for example, at Pylle Hill Pecten valoniensis 

 and Avicula contorta co-occur in h, that is, at the bottom of II ; 

 while Pecten valoniensis and Schizodus Ewaldi co-occur in i, that 

 is, at the bottom of IV). The vertebrates occur throughout the 

 entire Lower llhaotic, and even extend into the Upper Series (for 

 instance, in i at Pylle Hill) ; while in certain sections it is almost, 

 impossible to fix even the position of tlfeir maximum. 



Unfortunately, it has not been the general practice to estimate 

 the maximum of a species, but merely to register its occurrence in 

 each bed without any remark on its relative abundance. For this 

 reason, the comparison of the various sections loses a great part of 

 its value ; for a straggler which has escaped notice at one section 



