THE FOSSIL FLORA OF THE SOUTH WALES COAL FIELD. 571 



abundant, but no one would be justified in ignoring all other evidence, and to declare 

 that these rocks were Lower Coal Measures, simply because an isolated example of 

 Alethopteris lonchitica had been found in them. This unfortunately is practically what 

 in some cases has been done. 



General Kemarks on the Tables of Distribution. 



Before giving a synopsis of the species occurring in the South Wales Coal Field, 

 with the object of showing the relationship of the Upper Pennant Series, the Lower 

 Pennant Series, and the White Ash Series (the beds from which the fossils were 

 derived) to the generally recognised Upper, Middle, and Lower Coal Measures of 

 Britain, I append three tables, Nos. I. -III., devoting one to each of the three divisions 

 of the South Wales Coal Field; and, in connection with this subject, I add two other 

 tables, Nos. IV., V., showing the fossil plants of the New Rock Series and the Vobster 

 Series of the Somerset Coal Field, to indicate their probable position in regard to the 

 South Wales Coal Field. 



In the comparative tables I deal entirely with data derived from the British Coal 

 Fields : the wider question of their relation to the European Coal Fields must be deferred 

 till a future time. 



It is well, however, to take note here that although such strata as the Radstock and 

 Farrington Series of the Somerset Coal Field and the Forest of Dean Coal Field are 

 true members of the Upper Coal Measures as developed in Europe, they belong to 

 the lower part of the series : the upper beds, such as occur in certain parts of France, 

 being entirely absent from Britain. 



In the tables here given, there is one very important point which they do not bring 

 out, and one which cannot be ignored in correlating strata by the aid of their organic 

 remains, viz., the rarity or frequency of occurrence of the species. In the form in 

 which the tables are drawn up, all the records appear of equal value, it having been 

 found difficult to introduce a form of tabulation which would indicate the frequency or 

 rarity of the recorded species. 



As a case in point, we may again take Alethopteris lonchitica and Alethopteris Serlii 

 as two good examples to illustrate this. Aleth. lonchitica is found in the Upper, 

 Middle, and Lower Coal Measures: in the Upper Coal Measures it is a very rare 

 fossil, being one of the rarest in that series ; whereas in the Middle and Lower Coal 

 Measures it is one of the most common species. 



In the Upper Coal Measures of the Somerset Coal Field (the Radstock and 

 Farrington Series) and the Forest of Dean Coal Field, Aleth. Serlii occurs in extra- 

 ordinary abundance ; whereas in the Middle Coal Measures it is extremely rare, only a 

 very small number of specimens from this horizon having come under my notice ; and 

 from the Lower Coal Measures it appears to be entirely absent. Therefore, in reading 

 the tables, these remarks must be kept in view. 



