J. E. Marr—The Skiddad~Shtes. 125 



attempt to map the Skiddaw Slates according to their zones will 

 be fraught with unusual difficulty, and can only be accomplished by 

 a local observer with much time at his disposal through a term of 

 many years. Even then, the work will hai'dly repay the labour, 

 for the zonal succession of the equivalents of the Skiddaw Slates 

 will doubtless be discovered in other areas, where the slighter dis- 

 turbance of the rocks will i-ender the task one of comparative 

 simplicity. This being the case we may at once proceed to discover 

 what may be learnt from an examination of our present list. 



In studying it we may gain much information from noticing the 

 species which occur together on the same slab of stone (see p. 130), 

 and also by observing what species are absent from particular 

 localities. 



In Prof. Lapworth's paper on the Geological Distribution of the 

 Khabdophora ^ the Skiddaw Slates are divided into an Upper and a 

 Lower Group, but we require still further sub-divisions. These sub- 

 divisions will be considered in order, beginning with the oldest beds. 



1. Tremadoc Beds. 



Bryograptus Beds. — In Mr. Postlethwaite's collection is a slab (see 

 p. 130), of black slate from Barf, covered with numerous specimens 

 of Bryograptus ramosus, Brogger. The slab is shown natural size 

 in Fig. 1, p. 130, whilst Fig. 2, is a representation of one of the 

 Graptolites upon it enlarged two diameters. Another slab was 

 discovered by Miss Serjeant, of Girton College, at the same place, 

 and is now in the Woodwardian Museum. It bears fewer Grapt- 

 olites, but they are in a better state of preservation. Fig. 3, shows 

 the proximal portion of one of the Graptolites with a filiform 

 process from the proximal end of the sicula, whilst Fig. 4, repre- 

 sents another Graptolite from the same slab, which is further 

 enlarged in Fig. S, to exhibit the impression of the virgula. The 

 Graptolite figured by Salter^ under the name " Branchlet of Dicho- 

 grapsus " appears to belong to this species. 



A specimen collected at Barf by Mr. E. H. Tetley, of Trinity 

 College, and delineated in Fig. 6, possesses the characters of Bryo- 

 graptus Callavei, Lapw. The specimen is incomplete, and shows 

 fragments of four stipes only, but there is little doubt that it is 

 referable to this form. 



These specimens indicate the Tremadoc age of the beds contain- 

 ing them, for Bryograptus does not occur above this horizon.^ In 

 Norway Bryograptus ramosus is found low down amongst the re- 

 presentatives of the Tremadoc Slates, in the Lower Division of 

 the Ceratopygeschiefer, whilst Bryograptus Callavei occurs in the 

 Tremadoc Beds of the Shineton area. 



Bryograptus is not found associated with any other Graptolite on 

 the same slab in the Skiddaw Slates. Had it existed with the 



1 Ann. and Mag. Kat. Hist. ser. 5. vol. iii. 



2 Quart. Journ. Geol. Soc. vol. xix. p. 137, fig. 12. 



2 Tetragraptus fruticosus of Hall, with only four stipes, has no claim to be 

 included in the genus Bryograptus. 



