1867.] HALL NORTH DEYON FOSSILS. 371 



8. On the Relative Disteibution of Fossils throughout the North 

 Devon Series. By Townsend M. Hall, Esq., P.G.S. 



Contents. 



1. Introduction. 



2. Subdivision of the North Devon Rocks. 



3. Table of the Distribution of species throughout the various Fossiliferous 



G-roups. 



4. Note on the species of Lingula of Sloly Quarry. 



1. Introduction. 



Almost all observers since the time of Messrs. Weaver and "Williams, 

 in 1837 and 1838, have shown that the slates, shales, and sandstones 

 which constitute a large portion of the north of Devon differ so 

 much in their lithological and mineralogical structure as to render 

 it necessary to subdivide them into several successive zones or groups. 

 In the * Palaeozoic Fossils of Cornwall, Devon, and West Somerset,' 

 Prof. Phillips pointed out, by means of a synoptical table, the rela- 

 tive occurrence of fossils throughout these different subdivisions of 

 the North Devon series, which he named the Lynton, Combe Martin, 

 and Pilton groups respectively, each of these three fossiliferous 

 beds being separated from each other by a considerable thickness 

 of grits and shales, which have hitherto proved destitute of or- 

 ganic remains. More than a quarter of a century, however, has 

 now elapsed since Prof. Phillips's work was published ; and since 

 that date not only have many new fossil -localities been observed, 

 but so great a change has taken place in the system of nomenclature 

 as to render it at present anything but easy for the geologist to 

 identify the names of some of the species, or to ascertain in which 

 group they occur. Thus the Leptcena caperata of Phillips was 

 placed a few years later in the genus Strophalosia, and the name of 

 the species has since been altered into productoides, so that in 

 Strojphalosia productoides of the present day no trace whatever of 

 the original name can now be recognized. Again, many fossils, 

 especially the Brachiopoda, which, from imperfect material, were 

 supposed to constitute new species, and to require, therefore, a dis- 

 tinctive name, have lately been considerably reduced in number ; 

 and so great a diminution has been effected by Mr. Davidson, that 

 Spirifera disjuncta is now made to include the following North Devon 

 varieties, to which separate names had formerly been applied : — 

 S. Barumensis, S. calcarata, S. distans, S. extensa, S. gigantea, 

 S. g-randceva (?), S. pratensis, S. Verneuilii, and several others. In 

 the other classes of fossils the same reduction of species may eventually 

 be made. Several of the so-caUed species of Cucidlcea are probably 

 synonjnns ; and some of the crinoidal stems which abound in 

 the North Devon rocks are so doubtful as to render their specific 

 determination a matter of extreme difficulty. 



In order to insure as much accuracy as possible in the determina- 

 tion of my type specimens, I availed myself last autumn of the kind 

 assistance of Eobert Etheridge, Esq., F.G.S., Palaeontologist to the 

 Geological Survey, when, during the course of a visit to North Devon, 



